There are various techniques for synthesizing different Nanoparticles depending
upon the desired properties, application, etc. One of these widely applied techniques is
Hydrothermal. However, this technique is known for bulky materials and fabrication of
nano-scale materials requires adopting some strategies to alter the properties of materials
synthesized. We developed surface modification for this drawback. Application of surface
modifier, or surfactant, or capping agent, or organic ligands in proper concentration
could not only change morphology, reduce particle size, but also change the surface
chemistry of the nanoparticles fabricated. The ZnO and TiO2 nanoparticles were modified
using n-butylamine and caprylic acid as surface modifier under mild hydrothermal
conditions (p= autogenous, T= 150-250°C, and t= 18 h). The nanoparticles modified
were systematically characterized using Powder XRD, FTIR, SEM, zeta potential, and
BET surface area. The characterization results revealed that nanoparticles have small
size range, low agglomeration and highly stable.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2086

Mateki, A.

Shahmoradi, B.

Electronic Sumy State University Institutional Repository

400                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II            SURFACE MODIFICATION OF ZnO AND TiO2NANOPARTICLES UNDER MILD HYDROTHERMAL CONDITIONS Behzad Shahmoradi1,*,Afshin Maleki2  1 Environmental Health Research Center, Faculty of Health, Kurdistan 2 University of Medical Sciences, Sanandaj, Kurdistan-Iran  ABSTRACT There are various techniques for synthesizing different Nanoparticles depending upon the desired properties, application, etc. One of these widely applied techniques is Hydrothermal. However, this technique is known for bulky materials and fabrication of nano-scale materials requires adopting some strategies to alter the properties of materials synthesized. We developed surface modification for this drawback. Application of sur-face modifier, or surfactant, or capping agent, or organic ligands in proper concentration could not only change morphology, reduce particle size, but also change the surface chemistry of the nanoparticles fabricated. The ZnO and TiO2 nanoparticles were modi-fied using n-butylamine and caprylic acid as surface modifier under mild hydrothermal conditions (p= autogenous, T= 150-250°C, and t= 18 h). The nanoparticles modified were systematically characterized using Powder XRD, FTIR, SEM, zeta potential, and BET surface area. The characterization results revealed that nanoparticles have small size range, low agglomeration and highly stable.  Key words: surface modification, n-butylamine,caprylic acid,ZnO/TiO2 nanopar-ticles, hydrothermal conditions  INTRODUCTION Surface modification and characterization of naomaterials is a field of immense research potential for researchers worldwide for nearly half a century. Zinc oxide is a promising group II-VI oxide semiconductor showing quantum confinement effects at room temperature [1-3]. ZnO and TiO2 nanoparticles have broad applications such as UV absorption [4], deactivation of bacteria [5], photocatalysis of industrial effluents [6-7], etc. Furthermore, they are an envi-ronmentally friendly material, which are desirable especially for bio-applica-tions, such as bioimaging, cancer detection, and chemical sensors [8]. The photoactivity of zincite and titanium dioxide is generally detrimental for their application as photocatalyst or filler that oxidatively degrades, leading to embrittlement and chalking when exposed to sunlight or UV irradiation, especially in presence of moisture. Hence, some form of modification is im-                                               * e-mail: bshahmorady@gmail.comTel: (+98)9187705355 Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  401  plemented in order to reduce the surface photoactivity, to alter their hydropho-bic/hydrophilic character and improve their dispersibility in various media, to introduce new functional groups, which can react with organic molecules and enhance their compatibility with organics. Therefore, caprylic acid and n-butyl-amine were selected as surface modifiers to resolve the abovementioned prob-lems. The present authors have modified ZnO and TiO2 nanoparticles with these surfactants because they have low toxicity, eco-friendly, low density and low melting temperature. Most of the ZnO/TiO2 crystals have been synthesized by traditional high temperature solid-state method, which is energy consuming and difficult to con-trol the particle properties. ZnO/TiO2 nanoparticles can be prepared on a large scale at low cost by simple solution-based methods, such as chemical precipita-tion [9], sol-gel synthesis [10], and solvothermal/hydrothermal reaction [11, 12]. Hydrothermal technique is a promising alternative synthetic method because of the low process temperature and very easy to control the particle size. The hydro-thermal process has several advantages over other growth processes such as use of simple equipment, catalyst-free growth, low cost, large area uniform produc-tion, environmental friendliness and less hazardous [13]. EXPERIMENTALPREPARATION OF SURFACE MODIFIED ZNO/TIO2 NANOPARTICLES ZnOand TiO2 nanoparticles were modified under mild hydrothermal con-ditions (T=150 - 250°C, P =autogeneous). 1M of reagent grade ZnO/TiO2  (LobaChemie,  India)were  taken as  starting  material.  A certain  amount  of  1  N NaOH and HCl was added as mineralizer to the precursors respective-ly.Caprylic acid and n-butylamine (Sisco Research Lab PVT, Ltd., Mumbai, India)with different concentration (0.8, 1.0, 1.2, 1.4 and 1.6 ml)was added into the above-mentioned mixtures separately and it was stirred vigorously for a few minutes. The final mixture was then transferred to the Teflon liner (Vfill=15 ml), which was later placed inside a General-Purpose autoclaves. The autoclaves were provided with Teflon liners of 30 ml capacity. Then the assembled auto-clave was kept in an oven with a temperature programmer-controller. The tem-perature was programmed and kept at 150-250°C for 18 hr. After the experi-mental run, the autoclaves were cooled to the room temperature. The resultant product in the Teflon liner was then transferred in to a clean beaker and the product was washed with double distilled water. The surplus solution was re-moved using a syringe and the remnants were centrifuged for 20 minutes at 3000 rpm. The product was recovered and dried in a hot air oven at 50°C for a few hours. The dried particles were subjected to a systematic characterization using powder XRD, FTIR, SEM, Zeta potential and BET surface area meas-urement. 402                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II            CHARACTERIZATION OF THE SURFACE MODIFIED ZNO/TIO2 NANOPARTICLES The Powder X-ray diffraction patterns were recorded using Bruker, D8 Advance, Germany, with Cu KĮ, Ȝ 1 542ǖradiation, Voltage =30 kV, Current 15mA, Scan speed~5° min-1. The data were collected in the 2șrange 10-80°. The Fourier transform infrared (FTIR) spectra were recorded using FTIR, JASCO-460 PLUS, Japan, at resolution of 4 cm-1. SEM images of surface mod-ified ZnO hybrid nanoparticles were recorded using Hitachi, S-4200, Japan. Zeta potential and BET surface area was measured using Zetasizer 2000 in-strument (Malvern instruments), UK RESULTS AND DISCUSSION The powder XRD data reveals a highly crystallized wurtziteand ana-tasestructures  and  there  is  a  smallnew  peak,  which  may  be  corresponded  to  caprylic acid (Fig. 1). There is a slight change in the lattice parameters of sur-face modified ZnO/TiO2  nanoparticlesat a-axis and c-axis when compared to pure one (Table 1); this confirms the existence of surface modifier in ZnO/TiO2 hybrid nanoparticles.   Table 1– Cell parameters of modified ZnOand TiO2nanoparticles   Nanoparticles Surface modifi-er a ǖ) c ǖ) a c ratio V ǖ3) Ref  Pure ZnO Used ZnO ZnO ZnO PureTiO2 Used TiO2 TiO2 TiO2 NIL NIL Caprylic acid n-butylamine NIL NIL Caprylic acid n-butylamine 3 249 3 2556 3.2567 3.2435 3 7845 3.7918 3.7881 3.7837 5 207 5 2166 5.2021 5.1996 9 5143 9.5296 9.5230 9.4983 0 6239 0 6241 0.6260 0.6238 0 3977 0.3979 0.3978 0.3983 47 60 47 88 47.78 47.37 136 30 137.02 136.65 135.98 [17] pwa pw pw pw pw pw pw apw= Present work  Fig. 1 – Powder XRD patterns of ŷŷ pure nanoparticles without surfactant, surface modified using ŷŷn-butylamine and ŷŷcaprylic acid as surface modifier:  a) TiO2, b) ZnO Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  403  As Fig. 1 indicates, the presence of new peaks is more in the case of using HCl as solvent for surface modification of ZnO nanoparticles; these new peaks can be contributed to the presence of mixed phases of ZnO and ZnCl2. The modification with caprylic acid resulted in changing the crystal structure (Fig. 1). The functional groups present in the modified nanoparticles can be studied using FTIR spectroscopy. Fig. 2 shows the FTIR spectra of the reagent grade ZnO/TiO2, surface modified ZnO/TiO2 nanoparticles modified with n-butyla-mine and caprylic acid as surface modifier respectively. The intensity of the peaks was more when concentration of surface modifier was increased. The FTIR spectra of the modified nanoparticles show the presence of new peaks imply that the reagents were chemically immobilized on the surface of nanoparticles Thus, it can be concluded that theZnO/TiO2nanoparticles modified with the above said modifiers, have organic coverage on their surfaces, which has changed surface property of the nanoparticles. The absorption peaks corresponding to the presence of CH3, N-H, O-H, C O, etc. have been identified and illustrated in Fig. 2 [15].   Fig. 2 – FTIR spectra of ŷŷ reagent grade surface modified undoped hybrid  nanoparticles using ŷŷ caprylic acid, andŷŷn-butylamine: a) TiO2, b) ZnO.  Fig. 3 and Fig. 4 show characteristic SEM and HRSEM images of ZnO/TiO2 nanoparticles modified with (0 8 and 1 4 ml)n-butylamine and caprylic acid using 0.1 N NaOH and HCl as solvent.           Fig. 3 – Characteristic SEM images of surface modified TiO2 nanoparticles using NaOH as solvent: a) n-butylamine, and b) caprylic acid as surface modifier (a) (b) 404                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II             Fig. 4 – Characteristic SEM and HRSEM images of surface modified ZnO hybrid nanoparti-cles using: a) NaOH and n-butylamine as solvent and surface modifier respectively, b)NaOH and caprylic acid as solvent and surface modifier respectively, c) HCl and n-butylamine as solvent and surface modifier respectively, andd) HCl and caprylic acid as solvent and surface modifier respectively.  These figures show effect of the surface modifiers on the nanoparticles morphology.The agglomeration was less when a higher concentration of the surface modifier was used. The surface modification has led to the controlling of growth direction, also particle size and preventing agglomeration. It was found that the surface modifier could not only affect the dispersibility of the modified ZnOnanoparticles, but also change their morphology and size of the particles.The achieved morphology is quite suitable for the photodegradation purposes, since the ZnO/TiO2 nanoparticles are rounded, they can be more active in photodegradation of the organic pollutants presenting in the municipal and industrial effluents ZETA POTENTIAL OF SURFACE MODIFIED ZnO/TIO2 NANOPARTICLES Zeta (ȗ) potential measurement was performed for ZnO/TiO2 nanoparti-cles in order to characterize the surface charge of nanoparticles and Fig.  5 shows the result as a function of pH. The obtained ȗ potential of the nanoparti-Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  405  cles was found to decrease with increase of pH as is expected for a surface with acid-base group. The iso-electric point or point of zero charge (PZC) for ZnO nanoparticles was found to be 4.0 and 4.2 for modification by caprylic acid and n-butylamine respectively. For small enough nanoparticles, a high ȗ potential will confer stability, i.e. the solution or dispersion will resist aggregation. When the potential is low attraction exceeds repulsion and the dispersion will break and flocculate [16,17]. Therefore, colloids with high ȗ potential (negative or positive) are electrically stabilized while colloids with low zeta potentials tend to coagulate or flocculate. Our results indicate that the both surface modified nanoparticles are stable and highly negatively charged(at pH> 4.0 - 4.2) and this negative charge intensity is proportional to the increasing pH. On the other hand, the particles modified are positively charged at pH <4.0. The modified nanoparticles synthesized had low agglomeration, which prevents their floccu-lation or coagulation tendency. 2 4 6 8 10 12-40-30-20-100102030caprylic acidn-butylamineZeta Potential (meV)pH(a)2 4 6 8 10 12-40-30-20-1001020Zeta Potential (MeV)pHcaprylic acidn-butylamine(b) Fig. 5 – Zeta potential of surface modified a) TiO2 and b) ZnO nanoparticles  BET SURFACE AREA OF SURFACE MODIFIED ZnO/TIO2 NANOPARTICLES BET surface area was measured for the surface modified hybrid ZnOna-noparticulates using Malven 2000. It  was  found  that  the  BET  surface  area  is  5.630 and 4.513 m2/gfor surface modified ZnO hybrid nanoparticles using and n-butylamine and caprylic acid as surface modifier respectively.The BET sur-face area was found to be 15.928, 14.140 m2/g for surface modified TiO2 hybrid nanoparticles using n-butylamine and caprylic acid respectively. In both cases, NaOH was used as solvent.The results reveal thatn-butylamine makes the sur-face area more; the reason for having such low surface area can be contributed to the complex formation of ZnO nanoparticles with caprylic acid. It is known that surface modifiers are used to reduce agglomeration and hence reducing the particle size by controlling its growth direction. However, it was found that the affinity of ZnO nanoparticles to give bigger particles is proportional to the increasing concentration of the surfactant. Such phenomenon was not observed in the case of TiO2. 406                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II            EFFECT OF SOLVENT ON HYDROPHILICITY AND HYDROPHOBICITY One of the most important effects of surfactant on nanomaterials is chang-ing their hyrdophilicity property. Density of ZnO is high (about 7.0 g/m3) so that they are getting settle down quickly We observed that n-butylamine could make the nanoparticles highly hydrophilic, which is very favorable for photo-degradation purposes The reason is controlling the crystal growth, reducing agglomeration,and reducing density of the nanomaterials modified. The surface modification of the nanoparticles gives them an organic-inorganic hybrid so that the nanoparticles with desired properties can be fabricated It was also observed that  when HCl  was  used  as  solvent  in  modification  of  ZnO in  pres-ence of caprylic acid, it made the nanoparticles highly hydrophobic while using NaOH as solvent in presence of caprylic acid made the ZnO hybrid nanopartic-ulates hydrophilic and reduced density of the nanoparticulates modified. How-ever, both surfactants gave hydrophilic property to TiO2 nanoparticles. Reduc-tion of density was directly proportional to the concentration of the surface modifier (i.e. caprylic acid) added. Such interesting hydrophobic and hydro-philic properties of the ZnOnanoparticulates have been shown in Figs. 6-8.     Fig. 6 – Effect of caprylic acid concentration on density and in turn hydrophilicity of the ZnO nanoparticles using NaOH as solvent a)0 6 mL, b) 0 8 mL, c) 1.0 mL, and d)  1.2 mL caprylic acid   Fig. 7 – Effect of caprylic acid concentra-tion on density and in turn hydrophobicity of the ZnO nanoparticles using HCl as solvent and caprylic acid as surface modi-fier Fig. 8 – Effect of surfactant on hyrophilic-ity property of TiO2nanopar-ticles:  a) using n-butylamine as surface modifier and b) without surface modifier Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  407  It seems HCl reacts with ZnO and give highly low dense mixed phases of ZnCl2 and ZnO, which their density is less than water, which made them float at the surface of the water as a separate supernatant powder. CONCLUSIONS Surface modified ZnO/TiO2 nanoparticles were successfully carried out under mild hydrothermal conditions. Caprylic acid and n-butylamine were used as surface modifier separately. Surface modification changed morphology and size of the ZnO/TiO2 hybrid nanoparticles modified. In addition, it changed the surface charges and increased stability of the nanoparticles, which is necessary to achieve higher photodegradation efficiency. Using suitable solvent with respect to the precursors is an important factor in obtaining desired properties. Surface modifier along with solvent could give hydrophilic or hydrophobic property to the in situ surface modified ZnO hybrid nanoparticles. The results revealed that both caprylic acid and n-butylamine could be used for surface modification of ZnO particles. The strategy applied for surface modification could not only reduce agglomeration but also enhance the ZnO nanoparticles dispercibility.  REFERENCES [1] M. Zamfirescu, A. Kavokin, B. Gil et al. Phys. Rev. B., 65 (2002) 161205.  [2] S.W. Jung, W.I. Park, H.D. Cheong, G.C. Yi. Appl. Phys. Lett. 80 (2002) 1924.  [3] K.J. Klabunde, Ed., Nanoscale Materials in Chemistry. Wiley-Interscience, New York, 2001. [4] L. Sanchez, J. Peral, X. Domenech. ElectroChim. Acta. 41 (1996) 1981-1985.  [5] Z. Huang, X. Zheng, D. Yan. Et al. Langmuir, 24 (2008) 4140-4144. [6] L. Wang, H. Wei, Y. Fan et al. Nanoscale Res. Lett. 4 (2009) 558-564. [7] J. Lahiri, M. Batzill. J. Phys. Chem. C. 112 (2008) 4304-4307. [8] R. Hong, T. Pan, J. Qian, H. Li. Chem. Eng. J. 119 (2006) 71-81. [9] U. Narkiewicz, D. Sibera, I. Kuryliszyn-Kudelska et al. ActaPhysicaPolonica A. 113(2008) 1695-1700. [10]  A.R. Bari, M.D. Shinde, V. Deo, L.A. Patil. Indian J. Pure & Appl. Phys. 47 (2009) 24-27. [11] B. Shahmoradi, K. Soga, S. Ananda et al. Nanoscale, 2 (2010) 1160-1164. [12] B. Shahmoradi, I.A. Ibrahim, K. Namratha et al. IJCER, 2 (2010) 107-117. [13] K. Byrappa, M. Yoshimura, Handbook of Hydrothermal Technology, Noyes Publications/William Andrew Publishing LLC, U.S.A. 2001. [14] L.N. Dem’yanets, D.V. Kostomarov, I.P. Kuz’mina. Inorganic Materials, 38 (2002) 124–131. [15] L.P. Donald, M.L. Gary, S.K. George, Infrared spectroscopy. In Introduction to Spectroscopy, Thomson Learning: 3rd Ed. USA, 2001. pp. 13-101.  [16] Zeta Potential of Colloids in Water and Waste Water, ASTM Standard D 4187-82, American Society for Testing and Materials, 1985. [17] J. Lyklema, Fundamentals of Interface and Colloid Science. Elsevier, Wa-geningen, 1995.   

Surface modification of ZnO and Ti02 nanoparticles under mild hydrothermal conditions

SocioEconomic Challenges Journal (Sumy State University)

400                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II           
 
SURFACE MODIFICATION OF ZnO AND 
TiO2NANOPARTICLES UNDER MILD HYDROTHERMAL 
CONDITIONS 
Behzad Shahmoradi1,*,Afshin Maleki2 
 
1 Environmental Health Research Center, Faculty of Health, Kurdistan 
2 University of Medical Sciences, Sanandaj, Kurdistan-Iran 
 
ABSTRACT 
There are various techniques for synthesizing different Nanoparticles depending 
upon the desired properties, application, etc. One of these widely applied techniques is 
Hydrothermal. However, this technique is known for bulky materials and fabrication of 
nano-scale materials requires adopting some strategies to alter the properties of materials 
synthesized. We developed surface modification for this drawback. Application of sur-
face modifier, or surfactant, or capping agent, or organic ligands in proper concentration 
could not only change morphology, reduce particle size, but also change the surface 
chemistry of the nanoparticles fabricated. The ZnO and TiO2 nanoparticles were modi-
fied using n-butylamine and caprylic acid as surface modifier under mild hydrothermal 
conditions (p= autogenous, T= 150-250°C, and t= 18 h). The nanoparticles modified 
were systematically characterized using Powder XRD, FTIR, SEM, zeta potential, and 
BET surface area. The characterization results revealed that nanoparticles have small 
size range, low agglomeration and highly stable. 
 
Key words: surface modification, n-butylamine,caprylic acid,ZnO/TiO2 nanopar-
ticles, hydrothermal conditions 
 
INTRODUCTION 
Surface modification and characterization of naomaterials is a field of 
immense research potential for researchers worldwide for nearly half a century. 
Zinc oxide is a promising group II-VI oxide semiconductor showing quantum 
confinement effects at room temperature [1-3]. ZnO and TiO2 nanoparticles 
have broad applications such as UV absorption [4], deactivation of bacteria [5], 
photocatalysis of industrial effluents [6-7], etc. Furthermore, they are an envi-
ronmentally friendly material, which are desirable especially for bio-applica-
tions, such as bioimaging, cancer detection, and chemical sensors [8]. 
The photoactivity of zincite and titanium dioxide is generally detrimental 
for their application as photocatalyst or filler that oxidatively degrades, leading 
to embrittlement and chalking when exposed to sunlight or UV irradiation, 
especially in presence of moisture. Hence, some form of modification is im-
                                               
* e-mail: bshahmorady@gmail.comTel: (+98)9187705355 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  401 
 
plemented in order to reduce the surface photoactivity, to alter their hydropho-
bic/hydrophilic character and improve their dispersibility in various media, to 
introduce new functional groups, which can react with organic molecules and 
enhance their compatibility with organics. Therefore, caprylic acid and n-butyl-
amine were selected as surface modifiers to resolve the abovementioned prob-
lems. The present authors have modified ZnO and TiO2 nanoparticles with 
these surfactants because they have low toxicity, eco-friendly, low density and 
low melting temperature. 
Most of the ZnO/TiO2 crystals have been synthesized by traditional high 
temperature solid-state method, which is energy consuming and difficult to con-
trol the particle properties. ZnO/TiO2 nanoparticles can be prepared on a large 
scale at low cost by simple solution-based methods, such as chemical precipita-
tion [9], sol-gel synthesis [10], and solvothermal/hydrothermal reaction [11, 12]. 
Hydrothermal technique is a promising alternative synthetic method because of 
the low process temperature and very easy to control the particle size. The hydro-
thermal process has several advantages over other growth processes such as use 
of simple equipment, catalyst-free growth, low cost, large area uniform produc-
tion, environmental friendliness and less hazardous [13]. 
EXPERIMENTALPREPARATION OF SURFACE MODIFIED ZNO/TIO2 
NANOPARTICLES 
ZnOand TiO2 nanoparticles were modified under mild hydrothermal con-
ditions (T=150 - 250°C, P =autogeneous). 1M of reagent grade ZnO/TiO2  
(LobaChemie,  India)were  taken as  starting  material.  A certain  amount  of  1  N 
NaOH and HCl was added as mineralizer to the precursors respective-
ly.Caprylic acid and n-butylamine (Sisco Research Lab PVT, Ltd., Mumbai, 
India)with different concentration (0.8, 1.0, 1.2, 1.4 and 1.6 ml)was added into 
the above-mentioned mixtures separately and it was stirred vigorously for a few 
minutes. The final mixture was then transferred to the Teflon liner (Vfill=15 ml), 
which was later placed inside a General-Purpose autoclaves. The autoclaves 
were provided with Teflon liners of 30 ml capacity. Then the assembled auto-
clave was kept in an oven with a temperature programmer-controller. The tem-
perature was programmed and kept at 150-250°C for 18 hr. After the experi-
mental run, the autoclaves were cooled to the room temperature. The resultant 
product in the Teflon liner was then transferred in to a clean beaker and the 
product was washed with double distilled water. The surplus solution was re-
moved using a syringe and the remnants were centrifuged for 20 minutes at 
3000 rpm. The product was recovered and dried in a hot air oven at 50°C for a 
few hours. The dried particles were subjected to a systematic characterization 
using powder XRD, FTIR, SEM, Zeta potential and BET surface area meas-
urement. 
402                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II           
 
CHARACTERIZATION OF THE SURFACE MODIFIED ZNO/TIO2 
NANOPARTICLES 
The Powder X-ray diffraction patterns were recorded using Bruker, D8 
Advance, Germany, with Cu KĮ, Ȝ 1 542ǖradiation, Voltage =30 kV, Current 
15mA, Scan speed~5° min-1. The data were collected in the 2șrange 10-80°. 
The Fourier transform infrared (FTIR) spectra were recorded using FTIR, 
JASCO-460 PLUS, Japan, at resolution of 4 cm-1. SEM images of surface mod-
ified ZnO hybrid nanoparticles were recorded using Hitachi, S-4200, Japan. 
Zeta potential and BET surface area was measured using Zetasizer 2000 in-
strument (Malvern instruments), UK 
RESULTS AND DISCUSSION 
The powder XRD data reveals a highly crystallized wurtziteand ana-
tasestructures  and  there  is  a  smallnew  peak,  which  may  be  corresponded  to  
caprylic acid (Fig. 1). There is a slight change in the lattice parameters of sur-
face modified ZnO/TiO2  nanoparticlesat a-axis and c-axis when compared to 
pure one (Table 1); this confirms the existence of surface modifier in ZnO/TiO2 
hybrid nanoparticles.  
 
Table 1– Cell parameters of modified ZnOand TiO2nanoparticles   
Nanoparticles Surface modifi-
er 
a 
ǖ) 
c 
ǖ) 
a c 
ratio 
V 
ǖ3) 
Ref  
Pure ZnO 
Used ZnO 
ZnO 
ZnO 
PureTiO2 
Used TiO2 
TiO2 
TiO2 
NIL 
NIL 
Caprylic acid 
n-butylamine 
NIL 
NIL 
Caprylic acid 
n-butylamine 
3 249 
3 2556 
3.2567 
3.2435 
3 7845 
3.7918 
3.7881 
3.7837 
5 207 
5 2166 
5.2021 
5.1996 
9 5143 
9.5296 
9.5230 
9.4983 
0 6239 
0 6241 
0.6260 
0.6238 
0 3977 
0.3979 
0.3978 
0.3983 
47 60 
47 88 
47.78 
47.37 
136 30 
137.02 
136.65 
135.98 
[17] 
pwa 
pw 
pw 
pw 
pw 
pw 
pw 
apw= Present work 
 
Fig. 1 – Powder XRD patterns of ŷŷ pure nanoparticles without surfactant, surface 
modified using ŷŷn-butylamine and ŷŷcaprylic acid as surface modifier:  
a) TiO2, b) ZnO 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  403 
 
As Fig. 1 indicates, the presence of new peaks is more in the case of using 
HCl as solvent for surface modification of ZnO nanoparticles; these new peaks 
can be contributed to the presence of mixed phases of ZnO and ZnCl2. The 
modification with caprylic acid resulted in changing the crystal structure (Fig. 
1). The functional groups present in the modified nanoparticles can be studied 
using FTIR spectroscopy. Fig. 2 shows the FTIR spectra of the reagent grade 
ZnO/TiO2, surface modified ZnO/TiO2 nanoparticles modified with n-butyla-
mine and caprylic acid as surface modifier respectively. The intensity of the 
peaks was more when concentration of surface modifier was increased. The FTIR 
spectra of the modified nanoparticles show the presence of new peaks imply that 
the reagents were chemically immobilized on the surface of nanoparticles Thus, 
it can be concluded that theZnO/TiO2nanoparticles modified with the above said 
modifiers, have organic coverage on their surfaces, which has changed surface 
property of the nanoparticles. The absorption peaks corresponding to the presence 
of CH3, N-H, O-H, C O, etc. have been identified and illustrated in Fig. 2 [15]. 
 
 
Fig. 2 – FTIR spectra of ŷŷ reagent grade surface modified undoped hybrid  
nanoparticles using ŷŷ caprylic acid, andŷŷn-butylamine: a) TiO2, b) ZnO. 
 
Fig. 3 and Fig. 4 show characteristic SEM and HRSEM images of 
ZnO/TiO2 nanoparticles modified with (0 8 and 1 4 ml)n-butylamine and 
caprylic acid using 0.1 N NaOH and HCl as solvent.  
 
        
Fig. 3 – Characteristic SEM images of surface modified TiO2 nanoparticles using NaOH 
as solvent: a) n-butylamine, and b) caprylic acid as surface modifier 
(a) (b) 
404                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II           
 
 
Fig. 4 – Characteristic SEM and HRSEM images of surface modified ZnO hybrid nanoparti-
cles using: a) NaOH and n-butylamine as solvent and surface modifier respectively, b)NaOH 
and caprylic acid as solvent and surface modifier respectively, c) HCl and n-butylamine as 
solvent and surface modifier respectively, andd) HCl and caprylic acid as solvent and surface 
modifier respectively. 
 
These figures show effect of the surface modifiers on the nanoparticles 
morphology.The agglomeration was less when a higher concentration of the 
surface modifier was used. The surface modification has led to the controlling 
of growth direction, also particle size and preventing agglomeration. It was 
found that the surface modifier could not only affect the dispersibility of the 
modified ZnOnanoparticles, but also change their morphology and size of the 
particles.The achieved morphology is quite suitable for the photodegradation 
purposes, since the ZnO/TiO2 nanoparticles are rounded, they can be more 
active in photodegradation of the organic pollutants presenting in the municipal 
and industrial effluents 
ZETA POTENTIAL OF SURFACE MODIFIED ZnO/TIO2 
NANOPARTICLES 
Zeta (ȗ) potential measurement was performed for ZnO/TiO2 nanoparti-
cles in order to characterize the surface charge of nanoparticles and Fig.  5 
shows the result as a function of pH. The obtained ȗ potential of the nanoparti-
Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  405 
 
cles was found to decrease with increase of pH as is expected for a surface with 
acid-base group. The iso-electric point or point of zero charge (PZC) for ZnO 
nanoparticles was found to be 4.0 and 4.2 for modification by caprylic acid and 
n-butylamine respectively. For small enough nanoparticles, a high ȗ potential 
will confer stability, i.e. the solution or dispersion will resist aggregation. When 
the potential is low attraction exceeds repulsion and the dispersion will break 
and flocculate [16,17]. Therefore, colloids with high ȗ potential (negative or 
positive) are electrically stabilized while colloids with low zeta potentials tend 
to coagulate or flocculate. Our results indicate that the both surface modified 
nanoparticles are stable and highly negatively charged(at pH> 4.0 - 4.2) and this 
negative charge intensity is proportional to the increasing pH. On the other 
hand, the particles modified are positively charged at pH <4.0. The modified 
nanoparticles synthesized had low agglomeration, which prevents their floccu-
lation or coagulation tendency. 
2 4 6 8 10 12
-40
-30
-20
-10
0
10
20
30
caprylic acid
n-butylamine
Z
et
a 
Po
te
nt
ia
l (
m
eV
)
pH
(a)
2 4 6 8 10 12
-40
-30
-20
-10
0
10
20
Z
et
a 
Po
te
nt
ia
l (
M
eV
)
pH
caprylic acid
n-butylamine
(b)
 
Fig. 5 – Zeta potential of surface modified a) TiO2 and b) ZnO nanoparticles 
 
BET SURFACE AREA OF SURFACE MODIFIED ZnO/TIO2 
NANOPARTICLES 
BET surface area was measured for the surface modified hybrid ZnOna-
noparticulates using Malven 2000. It  was  found  that  the  BET  surface  area  is  
5.630 and 4.513 m2/gfor surface modified ZnO hybrid nanoparticles using and 
n-butylamine and caprylic acid as surface modifier respectively.The BET sur-
face area was found to be 15.928, 14.140 m2/g for surface modified TiO2 hybrid 
nanoparticles using n-butylamine and caprylic acid respectively. In both cases, 
NaOH was used as solvent.The results reveal thatn-butylamine makes the sur-
face area more; the reason for having such low surface area can be contributed 
to the complex formation of ZnO nanoparticles with caprylic acid. It is known 
that surface modifiers are used to reduce agglomeration and hence reducing the 
particle size by controlling its growth direction. However, it was found that the 
affinity of ZnO nanoparticles to give bigger particles is proportional to the 
increasing concentration of the surfactant. Such phenomenon was not observed 
in the case of TiO2. 
406                  Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II           
 
EFFECT OF SOLVENT ON HYDROPHILICITY AND HYDROPHOBICITY 
One of the most important effects of surfactant on nanomaterials is chang-
ing their hyrdophilicity property. Density of ZnO is high (about 7.0 g/m3) so 
that they are getting settle down quickly We observed that n-butylamine could 
make the nanoparticles highly hydrophilic, which is very favorable for photo-
degradation purposes The reason is controlling the crystal growth, reducing 
agglomeration,and reducing density of the nanomaterials modified. The surface 
modification of the nanoparticles gives them an organic-inorganic hybrid so 
that the nanoparticles with desired properties can be fabricated It was also 
observed that  when HCl  was  used  as  solvent  in  modification  of  ZnO in  pres-
ence of caprylic acid, it made the nanoparticles highly hydrophobic while using 
NaOH as solvent in presence of caprylic acid made the ZnO hybrid nanopartic-
ulates hydrophilic and reduced density of the nanoparticulates modified. How-
ever, both surfactants gave hydrophilic property to TiO2 nanoparticles. Reduc-
tion of density was directly proportional to the concentration of the surface 
modifier (i.e. caprylic acid) added. Such interesting hydrophobic and hydro-
philic properties of the ZnOnanoparticulates have been shown in Figs. 6-8.   
 
 
Fig. 6 – Effect of caprylic acid concentration on density and in turn hydrophilicity of the 
ZnO nanoparticles using NaOH as solvent a)0 6 mL, b) 0 8 mL, c) 1.0 mL, and d)  
1.2 mL caprylic acid 
  
Fig. 7 – Effect of caprylic acid concentra-
tion on density and in turn hydrophobicity 
of the ZnO nanoparticles using HCl as 
solvent and caprylic acid as surface modi-
fier 
Fig. 8 – Effect of surfactant on hyrophilic-
ity property of TiO2nanopar-ticles:  
a) using n-butylamine as surface modifier 
and b) without surface modifier 
Nanomaterials: Applications and Properties (NAP-2011). Vol. 2, Part II                  407 
 
It seems HCl reacts with ZnO and give highly low dense mixed phases of 
ZnCl2 and ZnO, which their density is less than water, which made them float 
at the surface of the water as a separate supernatant powder. 
CONCLUSIONS 
Surface modified ZnO/TiO2 nanoparticles were successfully carried out 
under mild hydrothermal conditions. Caprylic acid and n-butylamine were used 
as surface modifier separately. Surface modification changed morphology and 
size of the ZnO/TiO2 hybrid nanoparticles modified. In addition, it changed the 
surface charges and increased stability of the nanoparticles, which is necessary 
to achieve higher photodegradation efficiency. Using suitable solvent with 
respect to the precursors is an important factor in obtaining desired properties. 
Surface modifier along with solvent could give hydrophilic or hydrophobic 
property to the in situ surface modified ZnO hybrid nanoparticles. The results 
revealed that both caprylic acid and n-butylamine could be used for surface 
modification of ZnO particles. The strategy applied for surface modification 
could not only reduce agglomeration but also enhance the ZnO nanoparticles 
dispercibility.  
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Surface modification of ZnO and Ti02 nanoparticles under mild hydrothermal conditions

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