An Overview of Nanomaterials for Water and Wastewater Treatment

Review ArticleAn Overview of Nanomaterials for Water andWastewater Treatment

Haijiao Lu12 Jingkang Wang12 Marco Stoller3 Ting Wang12

Ying Bao12 and Hongxun Hao12

1National Engineering Research Center of Industry Crystallization Technology School of Chemical Engineering and TechnologyTianjin University Tianjin 300072 China2Co-Innovation Center of Chemical Science and Engineering Tianjin 300072 China3Department of Chemical Materials Sapienza University of Rome 00185 Rome Italy

Correspondence should be addressed to Hongxun Hao hongxunhaotjueducn

Received 26 April 2016 Revised 21 June 2016 Accepted 23 June 2016

Academic Editor Mikhael Bechelany

Copyright copy 2016 Haijiao Lu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Due to the exceptional characteristics which resulted from nanoscale size such as improved catalysis and adsorption properties aswell as high reactivity nanomaterials have been the subject of active research and developmentworldwide in recent yearsNumerousstudies have shown that nanomaterials can effectively remove various pollutants in water and thus have been successfully appliedin water and wastewater treatment In this paper the most extensively studied nanomaterials zero-valent metal nanoparticles (AgFe and Zn) metal oxide nanoparticles (TiO

2 ZnO and iron oxides) carbon nanotubes (CNTs) and nanocomposites are discussed

and highlighted in detail Besides future aspects of nanomaterials in water and wastewater treatment are discussed

1 Introduction

Generally speaking nanomaterials describe materials ofwhich the structural components are sized (in at least onedimension) between 1 and 100 nm [1] Due to the nanoscalesize of nanomaterials their properties such as mechanicalelectrical optical and magnetic properties are significantlydifferent from conventional materials A wide range of nano-materials have the characteristics of catalysis adsorption andhigh reactivity

In the past decades nanomaterials have been underactive research and development and have been successfullyapplied in many fields such as catalysis [2] medicine [3]sensing [4] and biology [5] In particular the applicationof nanomaterials in water and wastewater treatment hasdrawn wide attention Due to their small sizes and thus largespecific surface areas nanomaterials have strong adsorptioncapacities and reactivity What is more the mobility of nano-materials in solution is high [6] Heavy metals [7] organicpollutants [8] inorganic anions [9] and bacteria [10] havebeen reported to be successfully removed by various kinds

of nanomaterials On the basis of numerous studies nano-materials show great promise for applications in water andwastewater treatment At present the most extensivelystudied nanomaterials for water and wastewater treatmentmainly include zero-valent metal nanoparticles metal oxidesnanoparticles carbon nanotubes (CNTs) and nanocompos-ites

2 Nanomaterials for Water andWastewater Treatment

21 Zero-Valent Metal Nanoparticles211 Silver Nanoparticles Silver nanoparticles (Ag NPs) arehighly toxic tomicroorganisms and thus have strong antibac-terial effects against a wide range of microorganisms includ-ing viruses [11] bacteria [10] and fungi [12] As a goodantimicrobial agent silver nanoparticles have been widelyused for the disinfection of water

The mechanism of the antimicrobial effects of Ag NPsis not clearly known and remains under debate In recent

Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2016 Article ID 4964828 10 pageshttpdxdoiorg10115520164964828

2 Advances in Materials Science and Engineering

Live bacteria in

Blotter paper containingsilver nanoparticles

Dead bacteria out

Figure 1 Schematic presentation of the disinfection process ofblotter paper containing silver nanoparticles Reprinted from [19]with permission Copyright copy 2011 American Chemical Society

years several theories have been put forward Ag NPs havebeen reported to be able to adhere to the bacterial cell walland subsequently penetrate it resulting in structural changesof the cell membrane and thus increasing its permeability[13] Besides when Ag NPs are in contact with bacteria freeradicals can be generated They have the ability to damagethe cell membrane and are considered to cause the death ofcells [14] In addition as DNA contains abundant sulfur andphosphorus elements AgNPs can act with it and thus destroyit This is another explanation for the death of cells causedby Ag NPs [15] What is more the dissolution of Ag NPswill release antimicrobial Ag+ ions which can interact withthe thiol groups of many vital enzymes inactivate them anddisrupt normal functions in the cell [16]

With the development of nanotechnology Ag NPs havebeen successfully applied in water and wastewater disinfec-tion in recent years Direct application of Ag NPs mightcause some problems such as their tendency to aggregate inaqueous media that gradually reduces their efficiency duringlong-term use [17] Ag NPs attached to filter materials havebeen considered promising for water disinfection due to theirhigh antibacterial activity and cost-effectiveness [18]

Via the in situ reduction of silver nitrate Ag NPs havebeen deposited on the cellulose fibers of an absorbentblotting paper sheet (see Figure 1)TheAgNPs sheets showedantibacterial properties towards suspensions of Escherichiacoli and Enterococcus faecalis and inactivated bacteria duringfiltration through the sheet Moreover the silver loss fromthe Ag NPs sheets was lower than the standards for silverin drinking water put forward by Environmental ProtectionAgency (EPA) and World Health Organization (WHO) [19]Therefore for water contaminated by bacteria filtrationthrough paper deposited with Ag NPs could be an effectiveemergency water treatment Besides Ag NPs synthesized bychemical reduction have been incorporated into polyether-sulfone (PES) microfiltration membranes The activity ofmicroorganisms nearby the membranes was observed to be

Table 1 The standard reduction potentials of different metalsa

Metal Standard reduction potential (1198640V)Fe minus0440

Zn minus0762

Al minus1677

Ni minus0236

aThe data comes from [40]

remarkably suppressed The PES-Ag NPs membranes exhib-ited strong antimicrobial properties and held great potentialin application for water treatment [20]

In the past twenty years Ag NPs on ceramic materi-alsmembranes have drawn substantial attention due to theirdisinfection and biofouling reduction for household (point-of-use) water treatment [21] For instance the addition ofAg NPs to ceramic filters constructed with clay and sawdusthas turned out to be able to improve the removal efficiencyof Escherichia coli It was also found that filters with higherporosity achieved higher bacteria removal than those withlower porosity [22] Besides colloidal Ag NPs have beencombined with cylindrical ceramic filters which were madeup of clay-rich soil with water grog and flour in differentquantities and ways (dipping and painting) It was provedthat colloidal AgNPs improved the filter performance and thefilters can remove Escherichia coli in the rate between 978and 100 [23] Recently the attachment of AgNPs to ceramicmembranes has been successfully predicted by Derjaguin-Landau-Verwey-Overbeek (DLVO) approximation methods[24] Further studies on Ag NPs will promote their applica-tions in water and wastewater treatment

212 Iron Nanoparticles In recent years various zero-valentmetal nanoparticles such as Fe Zn Al and Ni in waterpollution treatment have drawn wide research interest Thestandard reduction potentials of Fe Al Ni and Zn are listedin Table 1 Due to the extremely high reductive ability nano-zero-valent Al is thermodynamically unstable in the presenceof water which favors the formation of oxideshydroxides onthe surface impeding (completely) the transfer of electronsfrom the metal surface to the contaminants [25] Comparedwith Fe Ni has a less negative standard reduction poten-tial indicating a lower reducing ability With a moderatestandard reduction potential nano-zero-valent Fe or Znholds good potential to act as reducing agents relative tomany redox-labile contaminants Despite a weaker reductionability Fe possesses many prominent advantages over Zn forapplications in water pollution treatment including excellentadsorption properties precipitation and oxidation (in thepresence of dissolved oxygen) and low cost Therefore zero-valent iron nanoparticles have been the most extensivelystudied zero-valent metal nanoparticles

As a result of the extremely small size and thus largespecific surface area nZVI possesses good adsorption prop-erties and strong reducing ability [26] These characteristicscontributemost to its excellent performance in the removal ofcontaminants Under anaerobic conditions as shown in (1)-(2) Fe0 can be oxidized by H

2O or H+ and generates Fe2+

Advances in Materials Science and Engineering 3

and H2 both of which are also potential reducing agents for

contaminants In the oxidation-reduction reaction betweennZVI and contaminants Fe2+ will be oxidized to Fe3+ whichcan form Fe(OH)

3with the increase of pH As a common

and effective flocculant Fe(OH)3facilitates the removal of

contaminants for example Cr(VI) [27] What is more ZVIcan degrade and oxidize a variety of organic compounds inthe presence of dissolved oxygen (DO) since ZVI transferstwo electrons to O

2to produce H

2O2(see (3)) The resultant

H2O2can be reduced to H

2O by ZVI (see (4)) Moreover the

combination of H2O2and Fe2+ (known as Fenton reaction)

can generate hydroxyl radicals (HO∙) which have strongoxidizing ability towards a wide range of organic compounds(see (5)) [28]

Fe0 + 2H2O 997888rarr Fe2+ +H

2+ 2OHminus (1)

Fe0 + 2H+ 997888rarr Fe2+ +H2

(2)

Fe0 +O2+ 2H+ 997888rarr Fe2+ +H

2O2

(3)

Fe0 +H2O2+ 2H+ 997888rarr Fe2+ + 2H

2O (4)

Fe2+ +H2O2997888rarr Fe3+ +HO∙ +OHminus (5)

With the effects of adsorption reduction precipitationand oxidation (in the presence of DO) nZVI has beensuccessfully applied in the removal of a large range of con-taminants including halogenated organic compounds [29]nitroaromatic compounds [30] organic dyes [31] phenols[32] heavy metals [33] inorganic anions such as phosphates[34] and nitrates [35] metalloids [36] and radio elements[37] What is more research on the application of nZVI inwater and wastewater treatment is not limited to water orlaboratory tests In recent years nZVI has also been appliedin soil remediation [38] and already achieved pilot-scale andfull-scale applications at real water contaminated field sites[39]

Despite many advantages nZVI also has its own dis-advantages such as aggregation oxidation and separationdifficulty from the degraded system To solve these problemsvarious modification approaches have been put forward toenhance the performance of nZVI in water and wastewatertreatment Commonmodification approachesmainly includedoping with other metals surface coating conjugation withsupports encapsulation in matrix and emulsification [41]Doping with other metals is supposed to enhance the reac-tivity of nZVI [42] Both surface coating and conjugationwith supports can prevent aggregation and enhance thedispersibility of nZVI [43 44] Besides both conjugationwith supports and encapsulation in matrix facilitate theseparation of nZVI from the degraded system [45 46] Inaddition the emulsification of nZVI is aimed at solving thedelivery problem of nZVI in dense nonaqueous phase liquid(DNAPL) [47]

213 Zinc Nanoparticles Although most studies on contam-inant degradation inwater andwastewater treatment by zero-valent metal nanoparticles have been focused on iron Znhas also been considered as an alternative [48] With a more

negative standard reduction potential (Table 1) Zn is astronger reductant compared with FeTherefore the contam-inant degradation rate of zinc nanoparticles may be fasterthan that of nZVI

For the application of nano-zero-valent zinc (nZVZ)most studies have been focused on dehalogenation reactionResearch indicated that the reduction rates of CCl

4by

nZVZ were more significantly affected by solution chemistrythan particle size or surface morphology By comparingthe reactivity of various types of nZVI and nZVZ it wasfound that nZVZ could degrade CCl

4more rapidly and com-

pletely than nZVI under favorable conditions [49] Besidesa study has been carried out to examine the degradationof octachlorodibenzo-p-dioxin (OCDD) in water with fourdifferent zero-valent metal nanoparticles zero-valent zinc(nZVZ) zero-valent iron (nZVI) zero-valent aluminum(nZVAL) and zero-valent nickel (nZVN) On the basisof experimental results only nZVZ was able to efficientlydegrade OCDD into lower chlorinated congeners and thusbecame the first reported zero-valent metal nanoparticlessuitable for OCDD dechlorination under ambient conditions[48]

However although several studies have demonstratedthat contaminant reduction by nZVZ could be successfulthe application of nZVZ is mainly limited in the degradationof halogenated organic compounds especially CCl

4 The

treatment of other kinds of contaminants by nZVZ has rarelybeen reported up to now Therefore pilot-scale or full-scaleapplications of nZVZhave not been achieved at contaminatedfield sites yet [49]

22 Metal Oxides Nanoparticles221 TiO2 Nanoparticles As an emerging and promis-ing technology photocatalytic degradation has attractedgreat attention since 1972 when Fujishima and Honda[50] observed electrochemical photolysis of water on TiO

2

semiconductor electrode In recent years photocatalyticdegradation technology has been successfully applied in thecontaminant degradation in water and wastewater At thepresence of light and catalyst contaminants can be graduallyoxidized into low molecular weight intermediate productsand eventually transformed into CO

2 H2O and anions such

as NO3

minus PO4

3minus and ClminusThe majority of common photocatalysts are metal oxide

or sulfide semiconductors among which TiO2has beenmost

extensively investigated in the past decades Owing to its highphotocatalytic activity reasonable price photostability andchemical and biological stability [51ndash53] TiO

2is the most

exceptional photocatalyst to date The large band gap energy(32 eV) of TiO

2requires ultraviolet (UV) excitation to induce

charge separation within the particles As shown in Figure 2upon UV irradiation TiO

2will generate reactive oxygen

species (ROS) which can completely degrade contaminantsin very short reaction time Besides TiO

2NPs show little

selectivity and thus are suitable for the degradation of allkinds of contaminants such as chlorinated organic com-pounds [54] polycyclic aromatic hydrocarbons [55] dyes[56] phenols [57] pesticides [58] arsenic [59] cyanide [60]


Figure 2 Schematic presentation of the mechanism of TiO2photo-

catalytic process Reprinted from [59] with permission Copyrightcopy 2014 American Chemical Society

and heavy metals [61] What is more hydroxyl radicalsgenerated under UV irradiation (120582 lt 400 nm) enable TiO

2

NPs to damage the function and structure of various cells[62] The photocatalytic properties of TiO

2NPs are able to

kill a wide array of microorganisms such as Gram-negativeand Gram-positive bacteria as well as fungi algae protozoaand viruses [63]

However TiO2NPs also have some disadvantages As

mentioned above their large band gap energy makes themneed the excitation of UV and the photocatalytic propertiesof TiO

2NPs under visible light are relatively inconspicu-

ous Hence studies have been conducted to improve thephotocatalytic properties of TiO

2NPs under visible light

and UV For example metal doping has been demonstratedto be able to improve the visible light absorbance of TiO

2

NPs [64] and increase their photocatalytic activity underUV irradiation [65] Among various metals Ag has receivedmuch attention formetal doping of TiO

2NPs because it could

enable the visible light excitation of TiO2NPs [66] and greatly

improve the photocatalytic inactivation of bacteria [67] andviruses [68] Besides modifications of TiO

2NPs by nonmetal

elements such as N F S and C have also been found to beable to narrow the band gap significantly enhance adsorptionin the visible region and improve the degradation of dyesunder visible light irradiation especially under natural solarlight irradiation [69]

Besides the production process of TiO2NPs is rather

complicated What is more it is difficult to recover TiO2NPs

from the treated wastewater especially when they are used insuspension In recent years more and more efforts have beendevoted to surmounting this problem Among them the cou-pling of the photocatalysis of TiO

2NPs with membrane tech-

nology has attracted much attention and shown promise forovercoming the recovery problem of TiO

2NPs A wide range

of membranes have been incorporated with TiO2NPs such

as poly(vinylidene fluoride) [70 71] polyethersulfone [7273] polymethyl methacrylate [74] and poly(amide-imide)[75] For instance usingNN1015840-methylenebisacrylamide as thecross-linker and ammonium persulphate as the initiator pairthe polymerization of acrylamide in an aqueous solution wascarried out to synthesize TiO

2poly[acrylamide-co-(acrylic

acid)] composite hydrogel Methylene blue was successfullyremoved by the photocatalysis of TiO

2NPs Moreover due

to the coupling with polymeric membranes TiO2NPs could

be easily separated from the treated system through a simplefiltration [76] A detailed review on TiO

2nanocomposite

based polymeric membranes has been presented [77] Morerecently doped TiO

2magnetic nanoparticles have been

synthesized in a spinning disk reactor to achieve a feasiblerecovery of the nanoparticles by a magnetic trap [78 79]The production process is continuous and thus suitable forindustrial applications [79]

222 ZnO Nanoparticles In the field of photocatalysis apartfrom TiO

2NPs ZnO NPs have emerged as another efficient

candidate in water and wastewater treatment because of theirunique characteristics such as direct and wide band gap inthe near-UV spectral region strong oxidation ability andgood photocatalytic property [80ndash82]

ZnO NPs are environment-friendly as they are com-patible with organisms [83] which makes them suitablefor the treatment of water and wastewater Besides thephotocatalytic capability of ZnO NPs is similar to that ofTiO2NPs because their band gap energies are almost the

same [84] However ZnONPs have the advantage of low costover TiO

2NPs [84] Moreover ZnO NPs can adsorb a wider

range of solar spectra and more light quanta than severalsemiconducting metal oxides [85]

Nevertheless similar to that of TiO2NPs the light

absorption of ZnO NPs is also limited in the ultravioletlight region due to their big band gap energies Besides theapplication of ZnONPs is impeded by photocorrosion whichwill result in fast recombination of photogenerated chargesand thus cause low photocatalytic efficiency [86]

To improve the photodegradation efficiency of ZnONPs metal doping is a common strategy Various types ofmetal dopants have been tested including anionic dopantscationic dopants rare-earth dopants and codopants [87]Besides many studies have shown that coupling with othersemiconductors such as CdO [88] CeO

2[89] SnO

2[90]

TiO2[91] graphene oxide (GO) [92] and reduced graphene

oxide (RGO) [93] is a feasible approach to enhance thephotodegradation efficiency of ZnO NPs

223 Iron Oxides Nanoparticles In recent years there is agrowing interest in the use of iron oxides nanoparticles for theremoval of heavymetal due to their simplicity and availabilityMagnetic magnetite (Fe

3O4) and magnetic maghemite (120574-

Fe2O4) and nonmagnetic hematite (120572-Fe

2O3) are often used

as nanoadsorbentsGenerally due to the small size of nanosorbent materials

their separation and recovery from contaminated water aregreat challenges for water treatment However magneticmagnetite (Fe

3O4) and magnetic maghemite (120574-Fe

2O4) can

be easily separated and recovered from the system with theassistance of an external magnetic field Therefore they havebeen successfully used as sorbent materials in the removal ofvarious heavy metals from water systems [94ndash96] In orderto increase adsorption efficiency and to avoid interferencefrom other metals ions iron oxides nanoparticles have


been functionalized to tune their adsorption properties byadding various ligands (eg ethylenediamine tetraacetic acid(EDTA) L-glutathione (GSH) mercaptobutyric acid (MBA)120572-thio-120596-(propionic acid) hepta(ethylene glycol) (PEG-SH)and meso-23-dimercaptosuccinic acid (DMSA)) [97] orpolymers (eg copolymers of acrylic acid and crotonic acid)[98] A flexible ligand shell has been reported to facilitatethe incorporation of a wide array of functional groups intothe shell and ensured the properties of Fe

3O4nanoparticles

are intact [99] Besides a polymer shell has been foundto be able to prevent aggregation of particles and improvethe dispersion stability of the nanostructures [98] Polymermolecules could act as binders formetal ions and thus becamea ldquocarrierrdquo of metal ions from treated water [99]

Hematite (120572-Fe2O3) has been considered as a stable

and cheap material in sensors catalysis and environmentalapplications [100] Moreover nanohematite has also beendemonstrated to be an effective adsorbent for the removal ofheavy metal ions from spiked tap water [101] 3D flower-like120572-Fe2O3microstructures assembled fromnanopetal subunits

have been synthesized for water treatment use The flower-like 120572-Fe

2O3could effectively prevent further aggregation

and the enhanced surface area withmultiple spaces and poresprovidedmany active sites to interact with contaminantsThemaximum adsorption capacities of the as-prepared 120572-Fe

2O3

for As(V) and Cr(VI) were much higher than those of manypreviously reported nanomaterials [100]

23 Carbon Nanotubes Carbon nanomaterials (CNMs) are aclass of fascinating materials due to their unique structuresand electronic properties which make them attractive forfundamental studies as well as diverse applications espe-cially in sorption processes Their advantages for water andwastewater treatment are due to (1) great capacity to adsorba wide range of contaminants (2) fast kinetics (3) largespecific surface area and (4) selectivity towards aromatics [6]There are several forms of CNMs such as carbon nanotubes(CNTs) carbon beads carbon fibers and nanoporous carbon[6] Among them CNTs have attracted the most attentionsand progressed rapidly in recent years

Carbon nanotubes are graphene sheets rolled up in cylin-ders with diameter as small as 1 nm [102] CNTs have attractedgreat interest as an emerging adsorbent due to their uniqueproperties With an extremely large specific surface areaand abundant porous structures CNTs possess exceptionaladsorption capabilities and high adsorption efficiencies fornumerous kinds of contaminants such as dichlorobenzene[103] ethyl benzene [104] Zn2+ [105] Pb2+ Cu2+ and Cd2+[106] and dyes [107] According to their (super)structuresCNTs can be classified into two types (Figure 3) (1) mul-tiwalled carbon nanotubes (MWCNTs) which comprisedmultiple layers of concentric cylinders with a spacing of about034 nm between the adjacent layers and (2) single-walledcarbon nanotubes (SWCNTs) which consist of single layersof graphene sheets seamlessly rolled into cylindrical tubes[108] In recent years bothMWCNTs [105ndash107] and SWCNTs[109] have been applied for the removal of contaminants inwater

To improve the adsorption mechanical optical and elec-trical properties carbon nanotubes are often combined withother metals or types of support [110] The functionalizationincreases the number of oxygen nitrogen or other groupson the surface of CNTs enhances their dispersibility andthus improves specific surface area [111ndash113] For examplea study using CNTs as a support for magnetic iron oxidehas been reported by Gupta et al [114] Combining theadsorption properties of CNTs with the magnetic propertiesof iron oxide a ldquocompositerdquo adsorbent was prepared toremove chromium from water Apart from owning excellentadsorption properties the ldquocompositerdquo adsorbent can beeasily separated from water via an external magnetic field

In spite of the exceptional properties of CNTs thedevelopment and applications of CNTs are mainly limitedby their low volume of production and high cost BesidesCNTs cannot be used alone without any supporting mediumor matrix to form structural components [102]

24 Nanocomposites As mentioned above every nanomate-rial has its own drawbacks For example nZVI has the disad-vantages of aggregation oxidation and separation difficultyfrom the degraded systemsThe light adsorption of TiO

2NPs

and ZnO NPs is limited in the ultraviolet light region dueto their big band gap energies Nanofiltration membranesare troubled by the problem of membrane fouling Carbonnanotubes are mainly limited by their low volume of pro-duction and high cost as well as the need for supportingmedium or matrix In order to overcome these problemsand achieve better removal efficiency it is a common andeffective strategy to fabricate nanocomposites for water andwastewater treatment

In recent years the synthesis of various nanocompositeshas become the most active subject in the field of nanoma-terials On the basis of numerous studies much progress hasbeen made throughout the world For example via chemicaldeposition of nZVI on CNTs a novel nanoscale adsorbentwas prepared According to the results the adsorbent hasgood potential for quick and effective removal of nitratein water Besides due to its unique magnetic property theadsorbent can be easily separated from the solution bythe magnet [115] Besides thin film nanocomposite (TFN)nanofiltration membranes have been prepared via in situinterfacial incorporation of TiO

2NPs along with fabrica-

tion of copolyamide network on a polyimide support Toimprove the compatibility of TiO

2NPs inside the polymer

matrix both amine and chloride compounds were utilizedto functionalize TiO

2NPs TFNmembranes exhibited higher

methanol flux and dye rejection in spite of lower swellingdegree The loading of TiO

2NPs turned out to be a crucial

factor on the NF membrane performance [116]In theory ideal composites for real applications should be

continuous bulk immobile materials of which the nanore-activity is obtained by anchoring or impregnating a parentmaterial structure with nanomaterials [117] What is moreit is widely acknowledged that the treatment of water andwastewater calls for nontoxic long-term stable and low-cost materials To obtain desirable nanocomposites furtherresearch is still under way


(a) (b)

Figure 3 (Super)structure representations of (a) MWCNTs and (b) SWCNTs Reprinted from [108] with permission Copyright copy 2009American Chemical Society

3 Conclusions and Perspectives

In this paper the most extensively studied nanomaterialszero-valent metal nanoparticles (Ag Fe and Zn) metaloxide nanoparticles (TiO

2 ZnO and iron oxides) carbon

nanotubes (CNTs) and nanocomposites were highlightedMoreover their applications in water and wastewater treat-ment were discussed in detail Considering the currentspeed of development and application nanomaterials lookextremely promising for water and wastewater treatment

However further studies are still needed to address thechallenges of nanomaterials Up to now only a few kindsof nanomaterials have emerged commercially Since lowproduction cost is crucial to ensure their wide spread appli-cations in water and wastewater treatment future researchshould be devoted to improving the economical efficiency ofnanomaterials Besides with increasingly extensive applica-tions of nanomaterials in water and wastewater treatmentthere are growing concerns on their potential toxicity to theenvironment and human health Available information inthe literature has revealed that several nanomaterials mayhave adverse effects on the environment and human health[118ndash120] Nevertheless standards for assessing the toxicityof nanomaterials are relatively insufficient at present Hencecomprehensive evaluation of the toxicity of nanomaterialsis in urgent need to ensure their real applications What ismore the evaluation and comparison of the performance ofvarious nanomaterials in water and wastewater treatment arestill short of uniform or recognized standards It is difficultto compare the performances of different nanomaterialsand figure out promising nanomaterials that deserve furtherdevelopment Therefore the performance evaluation mech-anism of nanomaterials in water and wastewater treatmentshould be perfected in the future

Competing Interests

The authors declare that there are no competing interestsregarding the publication of this paper

Acknowledgments

This research is financially supported byNationalNatural Sci-ence Foundation of China (no 21376165 and no 51478308)

References

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[2] V Parmon ldquoNanomaterials in catalysisrdquo Materials ResearchInnovations vol 12 no 2 pp 60ndash61 2008

[3] X-J Liang A Kumar D Shi and D Cui ldquoNanostructures formedicine and pharmaceuticalsrdquo Journal of Nanomaterials vol2012 Article ID 921897 2 pages 2012

[4] A Kusior J Klich-Kafel A Trenczek-Zajac K Swierczek MRadecka and K Zakrzewska ldquoTiO

2ndashSnO

2nanomaterials for

gas sensing andphotocatalysisrdquo Journal of the EuropeanCeramicSociety vol 33 no 12 pp 2285ndash2290 2013

[5] B Bujoli H Roussiere G Montavon et al ldquoNovel phosphatendashphosphonate hybrid nanomaterials applied to biologyrdquo Progressin Solid State Chemistry vol 34 no 2ndash4 pp 257ndash266 2006

[6] M M Khin A S Nair V J Babu R Murugan and SRamakrishna ldquoA review on nanomaterials for environmentalremediationrdquo Energy amp Environmental Science vol 5 no 8 pp8075ndash8109 2012

[7] W-W Tang G-M Zeng J-L Gong et al ldquoImpact ofhumicfulvic acid on the removal of heavymetals from aqueoussolutions using nanomaterials a reviewrdquo Science of the TotalEnvironment vol 468-469 pp 1014ndash1027 2014

[8] J Yan L HanWGao S Xue andM Chen ldquoBiochar supportednanoscale zerovalent iron composite used as persulfate activatorfor removing trichloroethylenerdquo Bioresource Technology vol175 pp 269ndash274 2015

[9] F Liu J H Yang J Zuo et al ldquoGraphene-supported nanoscalezero-valent iron removal of phosphorus from aqueous solutionand mechanistic studyrdquo Journal of Environmental Sciences vol26 no 8 pp 1751ndash1762 2014

[10] R S Kalhapure S J Sonawane D R Sikwal et al ldquoSolidlipid nanoparticles of clotrimazole silver complex an efficient


nano antibacterial against Staphylococcus aureus and MRSArdquoColloids and Surfaces B Biointerfaces vol 136 pp 651ndash658 2015

[11] B Borrego G Lorenzo J D Mota-Morales et al ldquoPotentialapplication of silver nanoparticles to control the infectivity ofRift Valley fever virus in vitro and in vivordquo NanomedicineNanotechnology Biology and Medicine vol 12 no 5 pp 1185ndash1192 2016

[12] C Krishnaraj R Ramachandran KMohan and P T Kalaichel-van ldquoOptimization for rapid synthesis of silver nanoparticlesand its effect on phytopathogenic fungirdquo Spectrochimica ActamdashPart A Molecular and Biomolecular Spectroscopy vol 93 pp95ndash99 2012

[13] I Sondi and B Salopek-Sondi ldquoSilver nanoparticles as antimi-crobial agent a case study on E coli as a model for Gram-negative bacteriardquo Journal of Colloid and Interface Science vol275 no 1 pp 177ndash182 2004

[14] M Danilczuk A Lund J Sadlo H Yamada and J MichalikldquoConduction electron spin resonance of small silver particlesrdquoSpectrochimica ActamdashPart A Molecular and Biomolecular Spec-troscopy vol 63 no 1 pp 189ndash191 2006

[15] K I Dhanalekshmi and K S Meena ldquoDNA intercalationstudies and antimicrobial activity of AgZrO

2corendashshell

nanoparticles in vitrordquo Materials Science and Engineering Cvol 59 pp 1063ndash1068 2016

[16] S Prabhu and E K Poulose ldquoSilver nanoparticles mechanismof antimicrobial action synthesis medical applications andtoxicity effectsrdquo International Nano Letters vol 2 no 1 p 322012

[17] X Li J J Lenhart and HWWalker ldquoAggregation kinetics anddissolution of coated silver nanoparticlesrdquo Langmuir vol 28no 2 pp 1095ndash1104 2012

[18] D V Quang P B Sarawade S J Jeon et al ldquoEffective waterdisinfection using silver nanoparticle containing silica beadsrdquoApplied Surface Science vol 266 pp 280ndash287 2013

[19] T A Dankovich and D G Gray ldquoBactericidal paper impreg-nated with silver nanoparticles for point-of-use water treat-mentrdquo Environmental Science and Technology vol 45 no 5 pp1992ndash1998 2011

[20] A M Ferreira E B Roque F V D Fonseca and C P BorgesldquoHigh flux microfiltration membranes with silver nanoparticlesfor water disinfectionrdquoDesalinationampWater Treatment vol 56no 13 pp 3590ndash3598 2015

[21] D Ren and J A Smith ldquoRetention and transport of silvernanoparticles in a ceramic porous medium used for point-of-use water treatmentrdquo Environmental Science and Technologyvol 47 no 8 pp 3825ndash3832 2013

[22] ENKallmanVAOyanedel-Craver and JA Smith ldquoCeramicfilters impregnated with silver nanoparticles for point-of-usewater treatment in rural guatemalardquo Journal of EnvironmentalEngineering vol 137 no 6 pp 407ndash415 2011

[23] V A Oyanedel-Craver and J A Smith ldquoSustainable colloidal-silver-impregnated ceramic filter for point-of-use water treat-mentrdquo Environmental Science and Technology vol 42 no 3 pp927ndash933 2008

[24] A M Mikelonis S Youn and D F Lawler ldquoDLVO approxima-tion methods for predicting the attachment of silver nanoparti-cles to ceramic membranesrdquo Langmuir vol 32 no 7 pp 1723ndash1731 2016

[25] M Rivero-Huguet and W D Marshall ldquoReduction of hex-avalent chromium mediated by micron- and nano-scale zero-valent metallic particlesrdquo Journal of Environmental Monitoringvol 11 no 5 pp 1072ndash1079 2009

[26] L J Matheson and P G Tratnyek ldquoReductive dehalogenationof chlorinated methanes by iron metalrdquo Environmental Scienceand Technology vol 28 no 12 pp 2045ndash2053 1994

[27] YWang Z Fang Y Kang and E P Tsang ldquoImmobilization andphytotoxicity of chromium in contaminated soil remediated byCMC-stabilized nZVIrdquo Journal ofHazardousMaterials vol 275pp 230ndash237 2014

[28] F Fu D D Dionysiou and H Liu ldquoThe use of zero-valentiron for groundwater remediation and wastewater treatment areviewrdquo Journal of Hazardous Materials vol 267 pp 194ndash2052014

[29] D-W Liang Y-H Yang W-W Xu S-K Peng S-F Lu andY Xiang ldquoNonionic surfactant greatly enhances the reductivedebromination of polybrominated diphenyl ethers by nanoscalezero-valent iron mechanism and kineticsrdquo Journal of Haz-ardous Materials vol 278 pp 592ndash596 2014

[30] Z Xiong B Lai P Yang Y Zhou J Wang and S Fang ldquoCom-parative study on the reactivity of FeCu bimetallic particles andzero valent iron (ZVI) under different conditions of N

2 air or

without aerationrdquo Journal of Hazardous Materials vol 297 pp261ndash268 2015

[31] G E Hoag J B Collins J L Holcomb J R Hoag M NNadagouda and R S Varma ldquoDegradation of bromothymolblue by lsquogreenerrsquo nano-scale zero-valent iron synthesized usingtea polyphenolsrdquo Journal of Materials Chemistry vol 19 no 45pp 8671ndash8677 2009

[32] X Y Wang M P Zhu H L Liu J Ma and F Li ldquoModificationof PdndashFe nanoparticles for catalytic dechlorination of 24-dichlorophenolrdquo Science of the Total Environment vol 449 pp157ndash167 2013

[33] M N Arancibia S E Baltazar A Garcıa et al ldquoNanoscalezero valent supported by Zeolite andMontmorillonite templateeffect of the removal of lead ion from an aqueous solutionrdquoJournal of Hazardous Materials vol 301 pp 371ndash380 2016

[34] Z Markova K M Siskova J Filip et al ldquoAir stable mag-netic bimetallic Fe-Ag nanoparticles for advanced antimicrobialtreatment and phosphorus removalrdquoEnvironmental Science andTechnology vol 47 no 10 pp 5285ndash5293 2013

[35] G G Muradova S R Gadjieva L Di Palma and G VilardildquoNitrates removal by bimetallic nanoparticles in waterrdquo Chemi-cal Engineering Transactions vol 47 pp 205ndash210 2016

[36] L Ling B Pan and W-X Zhang ldquoRemoval of seleniumfrom water with nanoscale zero-valent iron mechanisms ofintraparticle reduction of Se(IV)rdquo Water Research vol 71 pp274ndash281 2015

[37] L Ling and W-X Zhang ldquoEnrichment and encapsulationof uranium with iron nanoparticlerdquo Journal of the AmericanChemical Society vol 137 no 8 pp 2788ndash2791 2015

[38] M T Gueye L D Palma G Allahverdeyeva et al ldquoHexavalentchromium reduction by nano zero valent iron in soilrdquo ChemicalEngineering Transactions vol 47 pp 289ndash294 2016

[39] W-X Zhang ldquoNanoscale iron particles for environmentalremediation an overviewrdquo Journal of Nanoparticle Research vol5 no 3-4 pp 323ndash332 2003

[40] S G Bratsch ldquoStandard electrode potentials and temperaturecoefficients in water at 29815 Krdquo Journal of Physical and Chem-ical Reference Data vol 18 no 1 pp 1ndash21 1989

[41] M Stefaniuk P Oleszczuk and Y S Ok ldquoReview on nanozerovalent iron (nZVI) From synthesis to environmental appli-cationsrdquo Chemical Engineering Journal vol 287 pp 618ndash6322016


[42] Y H Liou S-L Lo C-J Lin W H Kuan and S C WengldquoChemical reduction of an unbuffered nitrate solution usingcatalyzed and uncatalyzed nanoscale iron particlesrdquo Journal ofHazardous Materials vol 127 no 1ndash3 pp 102ndash110 2005

[43] R Singh and V Misra ldquoStabilization of zero-valent ironnanoparticles role of polymers and surfactantsrdquo in Handbookof Nanoparticles pp 1ndash19 Springer New York NY USA 2015

[44] Z-X Chen X-Y Jin Z Chen M Megharaj and R NaiduldquoRemoval of methyl orange from aqueous solution usingbentonite-supported nanoscale zero-valent ironrdquo Journal ofColloid and Interface Science vol 363 no 2 pp 601ndash607 2011

[45] X Y Li L H Ai and J Jiang ldquoNanoscale zerovalent iron deco-rated on graphene nanosheets for Cr(VI) removal from aqueoussolution surface corrosion retard induced the enhanced per-formancerdquo Chemical Engineering Journal vol 288 pp 789ndash7972016

[46] X S Lv XQ Xue GM Jiang et al ldquoNanoscale zero-valent iron(nZVI) assembled on magnetic Fe

3O4graphene for chromium

(VI) removal from aqueous solutionrdquo Journal of Colloid ampInterface Science vol 417 pp 51ndash59 2014

[47] N D Berge and C A Ramsburg ldquoOil-in-water emulsions forencapsulated delivery of reactive iron particlesrdquo EnvironmentalScience amp Technology vol 43 no 13 pp 5060ndash5066 2009

[48] V Bokare J-L Jung Y-Y Chang and Y-S Chang ldquoReductivedechlorination of octachlorodibenzo-p-dioxin by nanosizedzero-valent zinc Modeling of rate kinetics and congener pro-filerdquo Journal of Hazardous Materials vol 250-251 pp 397ndash4022013

[49] P G Tratnyek A J Salter J T Nurmi and V Sarathy ldquoEnvi-ronmental applications of zerovalent metals iron vs zincrdquo inNanoscale Materials in Chemistry Environmental Applicationsvol 1045 of ACS Symposium Series chapter 9 pp 165ndash178 2010

[50] A Fujishima and K Honda ldquoElectrochemical photolysis ofwater at a semiconductor electroderdquo Nature vol 238 no 5358pp 37ndash38 1972

[51] K Guesh A Mayoral C M Alvarez Y Chebude and I DıazldquoEnhanced photocatalytic activity of TiO

2supported on zeolites

tested in real wastewaters from the textile industry of EthiopiardquoMicroporous and Mesoporous Materials vol 225 pp 88ndash972016

[52] K Imamura T Yoshikawa K Hashimoto and H KominamildquoStoichiometric production of aminobenzenes and ketonesby photocatalytic reduction of nitrobenzenes in secondaryalcoholic suspension of titanium(IV) oxide under metal-freeconditionsrdquoApplied Catalysis B Environmental vol 134-135 pp193ndash197 2013

[53] S B Rawal S Bera D Lee D-J Jang and W I Lee ldquoDesignof visible-light photocatalysts by coupling of narrow bandgapsemiconductors and TiO

2 effect of their relative energy band

positions on the photocatalytic efficiencyrdquo Catalysis Science andTechnology vol 3 no 7 pp 1822ndash1830 2013

[54] T Ohsaka K Shinozaki K Tsuruta and K Hirano ldquoPhoto-electrochemical degradation of some chlorinated organic com-pounds on n-TiO

2electroderdquo Chemosphere vol 73 no 8 pp

1279ndash1283 2008[55] M Guo W Song T Wang Y Li X Wang and X Du ldquoPhenyl-

functionalization of titanium dioxide-nanosheets coating fabri-cated on a titanium wire for selective solid-phase microextrac-tion of polycyclic aromatic hydrocarbons from environmentwater samplesrdquo Talanta vol 144 pp 998ndash1006 2015

[56] Y Lee S Kim P Venkateswaran J Jang H Kim and J KimldquoAnion co-doped Titania for solar photocatalytic degradationof dyesrdquo Carbon letters vol 9 no 2 pp 131ndash136 2008

[57] A T Nguyen C-T Hsieh and R-S Juang ldquoSubstituent effectson photodegradation of phenols in binary mixtures by hybridH2O2and TiO

2suspensions under UV irradiationrdquo Journal of

the Taiwan Institute of Chemical Engineers vol 62 pp 68ndash752016

[58] M G Alalm A Tawfik and S Ookawara ldquoComparison of solarTiO2photocatalysis and solar photo-Fenton for treatment of

pesticides industry wastewater operational conditions kinet-ics and costsrdquo Journal of Water Process Engineering vol 8 pp55ndash63 2015

[59] G Moon D Kim H Kim A D Bokare and W ChoildquoPlatinum-like behavior of reduced graphene oxide as a cocat-alyst on TiO

2for the efficient photocatalytic oxidation of

arseniterdquo Environmental Science amp Technology Letters vol 1 no2 pp 185ndash190 2014

[60] S H Kim S W Lee G M Lee B-T Lee S-T Yun and S-OKim ldquoMonitoring of TiO

2-catalytic UV-LED photo-oxidation

of cyanide contained in mine wastewater and leachaterdquo Chemo-sphere vol 143 pp 106ndash114 2016

[61] Z P Chen Y LiM Guo et al ldquoOne-pot synthesis ofMn-dopedTiO2grown on graphene and the mechanism for removal of

Cr(VI) and Cr(III)rdquo Journal of Hazardous Materials vol 310pp 188ndash198 2016

[62] A Mills and S Le Hunte ldquoAn overview of semiconductorphotocatalysisrdquo Journal of Photochemistry and Photobiology AChemistry vol 108 no 1 pp 1ndash35 1997

[63] H A Foster I B Ditta S Varghese and A Steele ldquoPho-tocatalytic disinfection using titanium dioxide spectrum andmechanism of antimicrobial activityrdquo Applied Microbiology andBiotechnology vol 90 no 6 pp 1847ndash1868 2011

[64] M Anpo S Kishiguchi Y Ichihashi et al ldquoThe design anddevelopment of second-generation titanium oxide photocata-lysts able to operate under visible light irradiation by applyinga metal ion-implantation methodrdquo Research on Chemical Inter-mediates vol 27 no 4-5 pp 459ndash467 2001

[65] W Mu J-M Herrmann and P Pichat ldquoRoom temperaturephotocatalytic oxidation of liquid cyclohexane into cyclohex-anone over neat and modified TiO

2rdquo Catalysis Letters vol 3

no 1 pp 73ndash84 1989[66] M K Seery R George P Floris and S C Pillai ldquoSilver doped

titanium dioxide nanomaterials for enhanced visible lightphotocatalysisrdquo Journal of Photochemistry and Photobiology AChemistry vol 189 no 2-3 pp 258ndash263 2007

[67] K Page R G Palgrave I P Parkin M Wilson S L P Savinand A V Chadwick ldquoTitania and silverndashtitania composite filmson glassmdashpotent antimicrobial coatingsrdquo Journal of MaterialsChemistry vol 17 no 1 pp 95ndash104 2007

[68] J-P Kim I-H Cho I-T Kim C-U Kim N H Heo and S-H Suh ldquoManufacturing of anti-viral inorganic materials fromcolloidal silver and titanium oxiderdquo Revue Roumaine de Chimievol 51 no 11 pp 1121ndash1129 2006

[69] C-C Liu Y-H Hsieh P-F Lai C-H Li and C-L Kao ldquoPho-todegradation treatment of azo dye wastewater by UVTiO

2

processrdquo Dyes and Pigments vol 68 no 2-3 pp 191ndash195 2006[70] Q Wang X Wang Z Wang J Huang and Y Wang ldquoPVDF

membranes with simultaneously enhanced permeability andselectivity by breaking the tradeoff effect via atomic layerdeposition of TiO

2rdquo Journal of Membrane Science vol 442 pp

57ndash64 2013


[71] S Meng J Mansouri Y Ye and V Chen ldquoEffect of tem-plating agents on the properties and membrane distillationperformance of TiO

2-coated PVDF membranesrdquo Journal of

Membrane Science vol 450 pp 48ndash59 2014[72] A Razmjou J Mansouri V Chen M Lim and R Amal ldquoTita-

nia nanocomposite polyethersulfone ultrafiltration membranesfabricated using a low temperature hydrothermal coating pro-cessrdquo Journal of Membrane Science vol 380 no 1-2 pp 98ndash1132011

[73] A Razmjou A R L Holmes H Li J Mansouri and V ChenldquoThe effect of modified TiO

2nanoparticles on the polyethersul-

fone ultrafiltration hollow fiber membranesrdquo Desalination vol287 pp 271ndash280 2012

[74] L M Hamming R Qiao P B Messersmith and L C BrinsonldquoEffects of dispersion and interfacial modification on themacroscale properties of TiO

2polymer-matrix nanocompos-

itesrdquo Composites Science and Technology vol 69 no 11-12 pp1880ndash1886 2009

[75] S Rajesh S Senthilkumar A Jayalakshmi M T Nirmala AF Ismail and D Mohan ldquoPreparation and performance eval-uation of poly (amidendashimide) and TiO

2nanoparticles impreg-

nated polysulfone nanofiltration membranes in the removal ofhumic substancesrdquoColloids and SurfacesA Physicochemical andEngineering Aspects vol 418 pp 92ndash104 2013

[76] W Kangwansupamonkon W Jitbunpot and S Kiatkamjorn-wong ldquoPhotocatalytic efficiency of TiO

2poly[acrylamide-co-

(acrylic acid)] composite for textile dye degradationrdquo PolymerDegradation and Stability vol 95 no 9 pp 1894ndash1902 2010

[77] E Bet-Moushoul Y Mansourpanah K Farhadi and MTabatabaei ldquoTiO

2nanocomposite based polymeric mem-

branes a review on performance improvement for variousapplications in chemical engineering processesrdquoChemical Engi-neering Journal vol 283 pp 29ndash46 2016

[78] O Sacco M Stoller V Vaiano P Ciambelli A Chianese andD Sannino ldquoPhotocatalytic degradation of organic dyes undervisible light on N-doped TiO

2photocatalystsrdquo International

Journal of Photoenergy vol 2012 Article ID 626759 8 pages2012

[79] M Stoller L Miranda and A Chianese ldquoOptimal feed locationin a spinning disc reactor for the production of TiO

2nanopar-

ticlesrdquo Chemical Engineering Transactions vol 17 pp 993ndash9982009

[80] A Janotti and C G Van de Walle ldquoFundamentals of zinc oxideas a semiconductorrdquo Reports on Progress in Physics vol 72 no12 Article ID 126501 2009

[81] D C Reynolds D C Look B Jogai C W Litton G Cantwelland W C Harsch ldquoValence-band ordering in ZnOrdquo PhysicalReview BmdashCondensedMatter andMaterials Physics vol 60 no4 pp 2340ndash2344 1999

[82] Y Chen D M Bagnall H-J Koh et al ldquoPlasma assistedmolecular beam epitaxy of ZnO on c-plane sapphire growthand characterizationrdquo Journal of Applied Physics vol 84 no 7pp 3912ndash3918 1998

[83] M L Schmidt and D J L MacManus ldquoZnO-nanostructuresdefects and devicesrdquoMaterials Today vol 10 pp 40ndash48 2007

[84] N Daneshvar D Salari and A R Khataee ldquoPhotocatalyticdegradation of azo dye acid red 14 in water on ZnO as analternative catalyst to TiO

2rdquo Journal of Photochemistry and

Photobiology A Chemistry vol 162 no 2-3 pp 317ndash322 2004[85] M A Behnajady N Modirshahla and R Hamzavi ldquoKinetic

study on photocatalytic degradation of CI Acid Yellow 23 by

ZnOphotocatalystrdquo Journal ofHazardousMaterials vol 133 no1ndash3 pp 226ndash232 2006

[86] C Gomez-Solıs J C Ballesteros L M Torres-Martınez et alldquoRapid synthesis of ZnO nano-corncobs from Nital solutionand its application in the photodegradation of methyl orangerdquoJournal of Photochemistry and Photobiology A Chemistry vol298 pp 49ndash54 2015

[87] K M Lee C W Lai K S Ngai and J C Juan ldquoRecent devel-opments of zinc oxide based photocatalyst in water treatmenttechnology a reviewrdquo Water Research vol 88 pp 428ndash4482016

[88] M Samadi A Pourjavadi and A Z Moshfegh ldquoRole ofCdO addition on the growth and photocatalytic activity ofelectrospun ZnO nanofibers UV vs visible lightrdquo AppliedSurface Science vol 298 pp 147ndash154 2014

[89] I-T Liu M-H Hon and L G Teoh ldquoThe preparationcharacterization and photocatalytic activity of radical-shapedCeO2ZnO microstructuresrdquo Ceramics International vol 40

no 3 pp 4019ndash4024 2014[90] M T Uddin Y Nicolas C Olivier et al ldquoNanostructured

SnO2-ZnO heterojunction photocatalysts showing enhanced

photocatalytic activity for the degradation of organic dyesrdquoInorganic Chemistry vol 51 no 14 pp 7764ndash7773 2012

[91] H R Pant C H Park B Pant L D Tijing H Y Kimand C S Kim ldquoSynthesis characterization and photocatalyticproperties of ZnO nano-flower containing TiO

2NPsrdquoCeramics

International vol 38 no 4 pp 2943ndash2950 2012[92] K Dai L Lu C Liang et al ldquoGraphene oxide modified ZnO

nanorods hybrid with high reusable photocatalytic activityunder UV-LED irradiationrdquo Materials Chemistry and Physicsvol 143 no 3 pp 1410ndash1416 2014

[93] X Zhou T Shi and H Zhou ldquoHydrothermal preparation ofZnO-reduced graphene oxide hybrid with high performance inphotocatalytic degradationrdquo Applied Surface Science vol 258no 17 pp 6204ndash6211 2012

[94] Y Lei F Chen Y Luo and L Zhang ldquoThree-dimensionalmagnetic graphene oxide foamFe

3O4nanocomposite as an

efficient absorbent for Cr(VI) removalrdquo Journal of MaterialsScience vol 49 no 12 pp 4236ndash4245 2014

[95] L Tan J Xu X Xue et al ldquoMultifunctional nanocompos-ite Fe

3O4SiO

2-mPDSP for selective removal of Pb(II) and

Cr(VI) from aqueous solutionsrdquo RSC Advances vol 4 no 86pp 45920ndash45929 2014

[96] A-F Ngomsik A Bee D Talbot and G Cote ldquoMagneticsolid-liquid extraction of Eu(III) La(III) Ni(II) and Co(II)with maghemite nanoparticlesrdquo Separation and PurificationTechnology vol 86 pp 1ndash8 2012

[97] C L Warner R S Addleman A D Cinson et al ldquoHigh-performance superparamagnetic nanoparticle-based heavymetal sorbents for removal of contaminants from naturalwatersrdquo ChemSusChem vol 3 no 6 pp 749ndash757 2010

[98] F Ge M-M Li H Ye and B-X Zhao ldquoEffective removalof heavy metal ions Cd2+ Zn2+ Pb2+ Cu2+ from aqueoussolution by polymer-modified magnetic nanoparticlesrdquo Journalof Hazardous Materials vol 211-212 pp 366ndash372 2012

[99] R A Khaydarov R R Khaydarov and O Gapurova ldquoWaterpurification from metal ions using carbon nanoparticle-conjugated polymer nanocompositesrdquo Water Research vol 44no 6 pp 1927ndash1933 2010

[100] H Liang B Xu and ZWang ldquoSelf-assembled 3D flower-like 120572-Fe2O3microstructures and their superior capability for heavy


metal ion removalrdquo Materials Chemistry and Physics vol 141no 2-3 pp 727ndash734 2013

[101] H J Shipley K E Engates andVAGrover ldquoRemoval of Pb(II)Cd(II) Cu(II) and Zn(II) by hematite nanoparticles effectof sorbent concentration pH temperature and exhaustionrdquoEnvironmental Science and Pollution Research vol 20 no 3 pp1727ndash1736 2013

[102] A Chatterjee and B L Deopura ldquoCarbon nanotubes andnanofibre an overviewrdquo Fibers and Polymers vol 3 no 4 pp134ndash139 2002

[103] X Peng Y Li Z Luan et al ldquoAdsorption of 12-dichlorobenzenefrom water to carbon nanotubesrdquo Chemical Physics Letters vol376 no 1-2 pp 154ndash158 2003

[104] C Lu F S Su and S Hu ldquoSurface modification of carbonnanotubes for enhancing BTEX adsorption from aqueoussolutionsrdquo Applied Surface Science vol 254 no 21 pp 7035ndash7041 2008

[105] H-H Cho K Wepasnick B A Smith F K Bangash D HFairbrother and W P Ball ldquoSorption of aqueous Zn[II] andCd[II] by multiwall carbon nanotubes the relative roles ofoxygen-containing functional groups and graphenic carbonrdquoLangmuir vol 26 no 2 pp 967ndash981 2010

[106] Y-H Li J Ding Z Luan et al ldquoCompetitive adsorption of Pb2+Cu2+ and Cd2+ ions from aqueous solutions by multiwalledcarbon nanotubesrdquo Carbon vol 41 no 14 pp 2787ndash2792 2003

[107] T Madrakian A Afkhami M Ahmadi and H BagherildquoRemoval of some cationic dyes from aqueous solutions usingmagnetic-modified multi-walled carbon nanotubesrdquo Journal ofHazardous Materials vol 196 pp 109ndash114 2011

[108] Y-L Zhao and J F Stoddart ldquoNoncovalent functionalizationof single-walled carbon nanotubesrdquo Accounts of ChemicalResearch vol 42 no 8 pp 1161ndash1171 2009

[109] C-M Yang J S Park K H An et al ldquoSelective removal ofmetallic single-walled carbon nanotubes with small diametersby using nitric and sulfuric acidsrdquo Journal of Physical ChemistryB vol 109 no 41 pp 19242ndash19248 2005

[110] P Z Ray and H J Shipley ldquoInorganic nano-adsorbents for theremoval of heavy metals and arsenic a reviewrdquo RSC Advancesvol 5 no 38 pp 29885ndash29907 2015

[111] A S Adeleye J R Conway K Garner Y Huang Y Su andA A Keller ldquoEngineered nanomaterials for water treatmentand remediation costs benefits and applicabilityrdquo ChemicalEngineering Journal vol 286 pp 640ndash662 2016

[112] Y-H Li S Wang J Wei et al ldquoLead adsorption on carbonnanotubesrdquo Chemical Physics Letters vol 357 no 3-4 pp 263ndash266 2002

[113] A S Adeleye and A A Keller ldquoLong-term colloidal stabilityand metal leaching of single wall carbon nanotubes effectof temperature and extracellular polymeric substancesrdquo WaterResearch vol 49 pp 236ndash250 2014

[114] V K Gupta S Agarwal and T A Saleh ldquoChromium removalby combining the magnetic properties of iron oxide withadsorption properties of carbon nanotubesrdquo Water Researchvol 45 no 6 pp 2207ndash2212 2011

[115] A Azari A-A Babaei R R Kalantary A Esrafili MMoazzenand B Kakavandi ldquoNitrate removal from aqueous solutionusing carbon nanotubes magnetized by nano zero-valent ironrdquoJournal of Mazandaran University of Medical Sciences vol 23no 2 pp 14ndash27 2014

[116] M Peyravi M Jahanshahi A Rahimpour A Javadi and SHajavi ldquoNovel thin film nanocomposite membranes incor-porated with functionalized TiO

2nanoparticles for organic

solvent nanofiltrationrdquo Chemical Engineering Journal vol 241pp 155ndash166 2014

[117] S J Tesh and T B Scott ldquoNano-composites for water remedi-ation a reviewrdquo Advanced Materials vol 26 no 35 pp 6056ndash6068 2014

[118] X Ma A Gurung and Y Deng ldquoPhytotoxicity and uptake ofnanoscale zero-valent iron (nZVI) by two plant speciesrdquo Scienceof the Total Environment vol 443 pp 844ndash849 2013

[119] X L Chen J OrsquoHalloran and M A K Jansen ldquoThe toxicity ofzinc oxide nanoparticles to Lemna minor (L) is predominantlycaused by dissolved ZnrdquoAquatic Toxicology vol 174 pp 46ndash532016

[120] F M Li Z Liang X Zheng W Zhao M Wu and Z Y WangldquoToxicity of nano-TiO

2on algae and the site of reactive oxygen

species productionrdquo Aquatic Toxicology vol 158 pp 1ndash13 2015

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Live bacteria in

Blotter paper containingsilver nanoparticles

Dead bacteria out

Figure 1 Schematic presentation of the disinfection process ofblotter paper containing silver nanoparticles Reprinted from [19]with permission Copyright copy 2011 American Chemical Society

years several theories have been put forward Ag NPs havebeen reported to be able to adhere to the bacterial cell walland subsequently penetrate it resulting in structural changesof the cell membrane and thus increasing its permeability[13] Besides when Ag NPs are in contact with bacteria freeradicals can be generated They have the ability to damagethe cell membrane and are considered to cause the death ofcells [14] In addition as DNA contains abundant sulfur andphosphorus elements AgNPs can act with it and thus destroyit This is another explanation for the death of cells causedby Ag NPs [15] What is more the dissolution of Ag NPswill release antimicrobial Ag+ ions which can interact withthe thiol groups of many vital enzymes inactivate them anddisrupt normal functions in the cell [16]

With the development of nanotechnology Ag NPs havebeen successfully applied in water and wastewater disinfec-tion in recent years Direct application of Ag NPs mightcause some problems such as their tendency to aggregate inaqueous media that gradually reduces their efficiency duringlong-term use [17] Ag NPs attached to filter materials havebeen considered promising for water disinfection due to theirhigh antibacterial activity and cost-effectiveness [18]

Via the in situ reduction of silver nitrate Ag NPs havebeen deposited on the cellulose fibers of an absorbentblotting paper sheet (see Figure 1)TheAgNPs sheets showedantibacterial properties towards suspensions of Escherichiacoli and Enterococcus faecalis and inactivated bacteria duringfiltration through the sheet Moreover the silver loss fromthe Ag NPs sheets was lower than the standards for silverin drinking water put forward by Environmental ProtectionAgency (EPA) and World Health Organization (WHO) [19]Therefore for water contaminated by bacteria filtrationthrough paper deposited with Ag NPs could be an effectiveemergency water treatment Besides Ag NPs synthesized bychemical reduction have been incorporated into polyether-sulfone (PES) microfiltration membranes The activity ofmicroorganisms nearby the membranes was observed to be

Table 1 The standard reduction potentials of different metalsa

Metal Standard reduction potential (1198640V)Fe minus0440

Zn minus0762

Al minus1677

Ni minus0236

aThe data comes from [40]

remarkably suppressed The PES-Ag NPs membranes exhib-ited strong antimicrobial properties and held great potentialin application for water treatment [20]

In the past twenty years Ag NPs on ceramic materi-alsmembranes have drawn substantial attention due to theirdisinfection and biofouling reduction for household (point-of-use) water treatment [21] For instance the addition ofAg NPs to ceramic filters constructed with clay and sawdusthas turned out to be able to improve the removal efficiencyof Escherichia coli It was also found that filters with higherporosity achieved higher bacteria removal than those withlower porosity [22] Besides colloidal Ag NPs have beencombined with cylindrical ceramic filters which were madeup of clay-rich soil with water grog and flour in differentquantities and ways (dipping and painting) It was provedthat colloidal AgNPs improved the filter performance and thefilters can remove Escherichia coli in the rate between 978and 100 [23] Recently the attachment of AgNPs to ceramicmembranes has been successfully predicted by Derjaguin-Landau-Verwey-Overbeek (DLVO) approximation methods[24] Further studies on Ag NPs will promote their applica-tions in water and wastewater treatment

212 Iron Nanoparticles In recent years various zero-valentmetal nanoparticles such as Fe Zn Al and Ni in waterpollution treatment have drawn wide research interest Thestandard reduction potentials of Fe Al Ni and Zn are listedin Table 1 Due to the extremely high reductive ability nano-zero-valent Al is thermodynamically unstable in the presenceof water which favors the formation of oxideshydroxides onthe surface impeding (completely) the transfer of electronsfrom the metal surface to the contaminants [25] Comparedwith Fe Ni has a less negative standard reduction poten-tial indicating a lower reducing ability With a moderatestandard reduction potential nano-zero-valent Fe or Znholds good potential to act as reducing agents relative tomany redox-labile contaminants Despite a weaker reductionability Fe possesses many prominent advantages over Zn forapplications in water pollution treatment including excellentadsorption properties precipitation and oxidation (in thepresence of dissolved oxygen) and low cost Therefore zero-valent iron nanoparticles have been the most extensivelystudied zero-valent metal nanoparticles

As a result of the extremely small size and thus largespecific surface area nZVI possesses good adsorption prop-erties and strong reducing ability [26] These characteristicscontributemost to its excellent performance in the removal ofcontaminants Under anaerobic conditions as shown in (1)-(2) Fe0 can be oxidized by H

2O or H+ and generates Fe2+







2to produce H






Fe0 + 2H2O 997888rarr Fe2+ +H

2+ 2OHminus (1)

Fe0 + 2H+ 997888rarr Fe2+ +H2

(2)

Fe0 +O2+ 2H+ 997888rarr Fe2+ +H

2O2

(3)

Fe0 +H2O2+ 2H+ 997888rarr Fe2+ + 2H

2O (4)







4by





4 The



2



as NO3

minus PO4




2is the most






2NPs show little






2


2NPs are able to








2





2NPs by nonmetal







2NPs A wide range





2NPs Moreover due



2nanocomposite














2[89] SnO

2[90]






2O3) are often used




2O4) can




3O4nanoparticles







2O3







2NPs













(a) (b)







Competing Interests


Acknowledgments


References





2ndashSnO

2nanomaterials for















2corendashshell

















2 air or




























































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials









2to produce H






Fe0 + 2H2O 997888rarr Fe2+ +H

2+ 2OHminus (1)

Fe0 + 2H+ 997888rarr Fe2+ +H2

(2)

Fe0 +O2+ 2H+ 997888rarr Fe2+ +H

2O2

(3)

Fe0 +H2O2+ 2H+ 997888rarr Fe2+ + 2H

2O (4)







4by





4 The



2



as NO3

minus PO4




2is the most






2NPs show little






2


2NPs are able to








2





2NPs by nonmetal







2NPs A wide range





2NPs Moreover due



2nanocomposite














2[89] SnO

2[90]






2O3) are often used




2O4) can




3O4nanoparticles







2O3







2NPs













(a) (b)







Competing Interests


Acknowledgments


References





2ndashSnO

2nanomaterials for















2corendashshell

















2 air or




























































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







2


2NPs are able to








2





2NPs by nonmetal







2NPs A wide range





2NPs Moreover due



2nanocomposite














2[89] SnO

2[90]






2O3) are often used




2O4) can




3O4nanoparticles







2O3







2NPs













(a) (b)







Competing Interests


Acknowledgments


References





2ndashSnO

2nanomaterials for















2corendashshell

















2 air or




























































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





3O4nanoparticles







2O3







2NPs













(a) (b)







Competing Interests


Acknowledgments


References





2ndashSnO

2nanomaterials for















2corendashshell

















2 air or




























































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)







Competing Interests


Acknowledgments


References





2ndashSnO

2nanomaterials for















2corendashshell

















2 air or




























































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










2corendashshell

















2 air or




























































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials


















































2




57ndash64 2013

























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



























2nanopar-



















2NPsrdquoCeramics








3O4SiO









































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

An Overview of Nanomaterials for Water and Wastewater Treatment