简介概要

Preparation, characterization, and adsorption-photocatalytic activity of nano TiO₂ embedded in diatomite synthesis materials

来源期刊：Rare Metals2017年第12期

论文作者：Ya-Li Zhang Jing Yang Xian-Jin Yu

文章页码：987 - 991

摘要：Nano TiO₂ embedded in diatomite（NTED）synthesis materials were prepared by a sol-gel method in absolute ethyl alcohol suspension. NTED synthesis materials have a higher specific surface area and larger pore volume using micromeritics ASAP 2020. The result of characterization was measured by X-ray diffraction（XRD）,Fourier transform infrared（FT-IR） spectroscopy, scanning electron microscope（SEM）, and energy dispersive spectroscopy（EDS）. The cyanide wastewater was employed to evaluate the adsorption capacity and photocatalytic activity of prepared NTED synthesis materials. The better photocatalytic activity and adsorption capacity of NTED synthesis materials are attributed to their high surface area and higher UV absorption intensity for the cyanide wastewater.

稀有金属(英文版) 2017,36(12),987-991

Preparation, characterization, and adsorption-photocatalytic activity of nano TiO₂ embedded in diatomite synthesis materials

Ya-Li Zhang Jing Yang Xian-Jin Yu

School of Chemical Engineering, Shandong University of Technology

收稿日期：8 August 2013

基金：financially supported by the National Natural Science Foundation of China (No.51304129);the Natural Science Foundation of Shandong Province (No. ZR2013EEM005);the High Education Science Technology Program of Shandong Province (No. J12LA04);

Preparation, characterization, and adsorption-photocatalytic activity of nano TiO₂ embedded in diatomite synthesis materials

Ya-Li Zhang Jing Yang Xian-Jin Yu

School of Chemical Engineering, Shandong University of Technology

Abstract：

Nano TiO₂ embedded in diatomite(NTED)synthesis materials were prepared by a sol-gel method in absolute ethyl alcohol suspension. NTED synthesis materials have a higher specific surface area and larger pore volume using micromeritics ASAP 2020. The result of characterization was measured by X-ray diffraction(XRD),Fourier transform infrared(FT-IR) spectroscopy, scanning electron microscope(SEM), and energy dispersive spectroscopy(EDS). The cyanide wastewater was employed to evaluate the adsorption capacity and photocatalytic activity of prepared NTED synthesis materials. The better photocatalytic activity and adsorption capacity of NTED synthesis materials are attributed to their high surface area and higher UV absorption intensity for the cyanide wastewater.

Keyword：

Nano TiO₂; Diatomite(NTED); Embedded; Adsorption; Photocatalysis;

Author： Ya-Li Zhang e-mail:zhangy10419@163.com ; Xian-Jin Yu e-mail:xjy@sdut.edu.cn;

Received： 8 August 2013

1 Introduction

Cyanide wastewater is harmful to the environment and living beings,especially because of containing heavy metal and cyanide.Nowadays,there are many technologies to treat the wastewater,such as [ 1, 2, 3] chlor-alkali oxidation method,H₂O₂ oxidation,acidification method,etc.However,those methods are complex,and the treatment effect is poor.Adsorption method [ 4] is widely used in the wastewater treatment,because it is cheaper and the treatment effect is better.But adsorption process only moves ion from the wastewater to adsorbent rather than get rid of the ion.In this study,another cheaper and higher effect material was prepared,and the material has both function of adsorption and photocatalytic activity for cyanide wastewater;cyanide can be decomposed rather than moved to other place only.Nanostructure titania,as a cheap nontoxic efficient photocatalyst,becomes the focus of numerous studies because of its attractive characteristics and application of the decomposition of environmental contaminants [ 5, 6] .In order to get the maximize photoactivity,the most commercial titanias are ultrafine powders and they have large surface area.However,the particles are so tiny that the separation and recovery of catalyst are difficult,and the particles trend to agglomerate into large particles,making against on catalyst performance.For this reason,many researchers have put much attention to mesoporous materials supporting TiO₂ photocatalyst,such as H₄Nb₆O₁₇ [ 7] :titania pillar was constructed in the interlayer of H₄Nb₆O₁₇ using titania sol;activated carbon [ 8] :titanium dioxide photocatalyst loaded onto activated carbon support using chemical vapor deposition;a glass matrix [ 9] :preparation of TiO₂ particulate films onto glass plate;optical fibers [ 10] :semitransparent WO₃ films can be used for photocatalytic solute degradation;and SiO₂ [ 11] :nano titania particles embedded in mesoporous silica.

It is desirable for a support to be of high thermal stability to present a high specific surface area and to be transparent to UV.Probably,it is the reason why most of studies immobilized photocatalyst are focused on the siliceous materials as supports.The methods of synthesizing nano TiO₂ embedded in diatomite (NTED) are as follows:hydrolysis method [ 12] ,micro emulsion method,and solgel method [ 13] .

In the present work,the synthesis of NTED by sol-gel method was investigated.The samples were fabricated by hydrolyzing butyl titanate in ethanol,and then the SiO₂ was coated and followed by heat treatment at different temperatures.The synthesized materials were characterized using micromeritics ASAP 2020,X-ray diffraction (XRD),Fourier transform infrared spectroscopy (FT-IR),scanning electron microscope (SEM),and energy dispersive spectroscopy (EDS).In this layer material,diatomite was expected to happen adsorption reaction (adsorbing Cu),and UV light irradiation was expected to induce the catalytic oxidation reaction (oxidizing cyanide) in the cyanide wastewater.For those reactions,the cyanide wastewater could be treated to up to national effluent standard.

2 Experimental

2.1 Sample preparation

Purified diatomite was obtained by adding concentrated sulfuric acid and a certain amount of distilled water,and boiling together for 1 h.Then,the diatomite was suction filtered and washed with distilled water to neutral.The purified diatomite was dried in vacuum at 100℃for 6 h.

The typical sol-gel synthesis of TiO₂-doped SiO₂ is in detail as below.The diatomite (5.0 g) was mixed with absolute ethyl alcohol (80 ml) and butyl titanate (18 ml),and the solution was kept mechanical rabbling to get a homogeneous mixture.A stoichiometric amount of hydrochloric acid in 60 ml of distilled water was added to the mixture cautiously and slowly under vigorous stirring.When the resulting mixture turned to be a sol,it was stirred for 5 h and aged for 1 day to form a gel.The gel was dried in the vacuum at 70℃for 24 h.The resulting power was calcined at different temperatures for 2 h.The different NTED syntheses were expressed.

2.2 Characterization

The XRD patterns of the NTED photocatalysts were recorded on an X-ray diffractometer using Cu Kαradiation as X-ray source.The diffractograms were recorded in the 2θrange of 10°-80°,and the particle size was determined from the broadening of diffraction peak.Brunauer-Emmett-Teller(BET) surface area,pore volume,and average pore diameter of the NTED photocatalysts were measured by N₂ physisorption at-196℃using micromeritics ASAP 2020 system.The FT-IR spectra were obtained on a FT-IR using KBr pellets.The SEM image was recorded using a scanning electron microscope (SEM).The component content of the NTED photocatalysts was obtained by EDS.

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Table 1 Physicochemical properties of TiO₂,SiO₂,and NTED pro-vided by micromeritics ASAP 2020 system

2.3 Adsorption and photocatalytic reaction

Adsorption and photocatalytic reaction were carried out in a Pyrex reactor which was attached to an inner radiation type 120 W high-pressure mercury lamp,containing 0.5 g sample and 10 ml of cyanide wastewater with Cu initial concentration of 870 mg·L^-1 and cyanogens initial concentration of 545 mg·L^-1.First,the mixture was stirred for1 h at the room temperature in dark,reaching the adsorption equilibrium;then,the mixture was placed to the Pyrex reactor by water cooled,and the mixture solution bubbled with air.The photoactivity of catalyst was determined by measuring the concentration of CN^-during the irradiation of the catalyst suspensions in the cyanide wastewater.In the cyanide wastewater,the adsorption of the synthesis was obtained by measuring the concentration of Cu during the irradiation of the catalyst suspensions.The concentration of copper was determined by flame atomic absorption spectrometry,and the concentration of cyanide ion was evaluated by silver nitrate titration method.

3 Results and discussion

3.1 Textural properties

Table 1 shows the textural properties and average crystal size calculated for these materials.From Table 1,it can be seen that the pure titanium dioxide sample,the BET surface area,Langmuir surface area,pore size,and the pore volumes are very small;but the BET surface area,Langmuir surface area,pore size,and the pore volumes of pure silica sample are70 times of pure titanium dioxide sample.The BET surface area,Langmuir surface area,pore size,and the pore volumes of the NTED synthesis are less than those of the pure silica sample,which indicates that part of TiO₂ particles disperse into the pores of silica,leading to the decrease of BET surface area,Langmuir surface area,pore size,and pore volume.

3.2 XRD results

The XRD patterns of NTED samples calcined at different temperatures (200,300,400,500,and 600℃) are shown in Fig.1.The peaks at 2θ=26.8°,and 36.8°are characteristic peaks of silica,which shows that silica is the primary composition of NTED.For NTED,the characteristic peaks of crystal TiO₂ are shown at 2θ=25.2°(101),37.7°(004),48.0°(200),etc. [ 14] ,which explains that the tiny grain deposited on surface of the diatomite is anatase.It can be seen from Fig.1 that the peaks of anatase phase become stronger and shaper as the temperature increases,and the characteristic peaks of crystal TiO₂ emerge above500℃.

Fig.1 XRD patterns of NTED calcined at different temperatures

Fig.2 FTIR spectrum of NTED

3.3 FT-IR results

Figure 2 shows the FT-IR spectra of the NTED after heating to 500℃.The peaks in the spectra were assigned according to the literature.The broad band in the region-1500-600 cm^-1 corresponds to the fundamental stretching vibrations of Ti-O band [ 15] .The peaks at 1,120,1,097,and 790 cm^-1 are characteristic of a silica network:the bands at 1,097 and 1,120 cm^-1 are ascribed to the LO and TO components of the asymmetric stretch of the SiO₄ unit,respectively;and the feature at 790 cm^-1 is due to the symmetric stretch of the SiO₄ unit [ 16] .The shoulder at978 cm^-1 is made up of contributions from Si-(OH)stretches and a Si-O-Ti vibration [ 17] .The band at1,650 cm^-1 corresponds to the H-O-H bending vibration of water.The broad band in the region of3,300-3,600 cm^-1 is assigned to the fundamental stretching vibrations of different hydroxy groups [ 18] .

Fig.3 EDS result of silica sample calcined at 500℃

Fig.4 EDS result of NTED synthesis calcined at 500℃

3.4 EDS results

Figures 3 and 4 are EDS spectra of diatomite and NTED synthesis.As shown in Fig.3,the diatomite is mainly composed of Si,O,Al,Na,Cl,Si;and Si,O elements content are outstanding.For NTED synthesis,the Ti element peaks may be seen from Fig.4.Because of Ti element in surface layer of the diatomite,intensities of Si,Al,and other elements peaks are obviously dropped,and the TiO₂ concentration of the composite obtained through EDS spectra is about 18.62%.

3.5 SEM results

Figure 5 shows the SEM images of diatomite and the NTED synthesis.As shown in Fig.5a,plentiful diatomaceous primitive hole can be observed,the aperture of which is tiny.As shown in Fig.5b,on the diatomite porous surface,the size of tiny grain is dispersed evenly in the diatomite porous surface [ 19] .This kind of micros truc ture is important to increase the active sites of the photochemical catalysis and improve the photochemical catalysis efficiency.It is the reason that we take the siliceous materials as supports.

Fig.5 SEM images of diatomite a and nano-TiO₂/diatomite synthesis b

Fig.6 Adsorption and photocatalytic activity of NTED

3.6 Adsorption and photocatalytic

The cyanide wastewater,which contains CN^-and Cu(Ⅱ),a kind of wastewater from a Gold Smelter of Shandong Province,was employed to evaluate the adsorption capacity and pho toc ataly tic activity of prepared NTED synthesis materials.

In photodegradation and adsorption experiments,there are two factors to be concerned in the decrease of the concentration of the cyanide wastewater:the adsorption of Cu(Ⅱ) on the surface of the synthesis and photodegradation of CN^-.

Figure 6 shows the curves of the CN^-and Cu(Ⅱ) by NTED synthesis materials at different times.During the initial 60 min without UV light,the concentrations of CN^-and Cu(Ⅱ) rapidly decrease due to the adsorption of the CN^-and Cu(Ⅱ) on the samples surface.After 45 min,the concentrations of CN^-and Cu(Ⅱ) slowly decrease,indicating that the adsorption reaches equilibrium nearly.However,after 60 min,the concentration of CN^-suddenly decreases rapidly with the UV irradiation,because of the photocatalysis of TiO₂ to CN^-.

After adsorption and photocatalytic,the NTED synthesis materials were filtered and dried,and then were taken desorption by 30%H₂SO₄ solution.However,after desorption,the stripping liquid are evaluated that the concentration of cyanide is practically to 0.So the photocatalytic activity of prepared NTED synthesis materials gets the desired results.

4 Conclusion

NTED synthesis materials were prepared by a sol-gel method in absolute ethyl alcohol suspension,and dried in the vacuum and then calcined at 500℃temperature for2h.

NTED synthesis materials show much higher adsorption capacity and photocatalytic activity for the cyanide wastewater,the Cu(Ⅱ) of adsorption capacity is 85%,and the CN^-of decomposition capacity is 90%for 0.5 g sample disposing of 10 ml cyanide wastewater.The better photocatalytic activity and adsorption capacity of NTED synthesis materials are attributed to their high surface area and higher UV absorption intensity for the cyanide wastewater.