魏 健,沈常宇,代 凱

(1.中國計(jì)量學(xué)院 光學(xué)與電子科技學(xué)院,浙江 杭州 310018;2.淮北師范大學(xué) 物理與電子信息學(xué)院,安徽 淮北 235000)

鉺摻雜二氧化鈦制備及其光催化性能研究

魏 健1,2,沈常宇1,代 凱2

(1.中國計(jì)量學(xué)院 光學(xué)與電子科技學(xué)院,浙江 杭州 310018;2.淮北師范大學(xué) 物理與電子信息學(xué)院,安徽 淮北 235000)

通過水熱合成法制備了二氧化鈦和稀土餌離子摻雜二氧化鈦光催化劑,并通過X射線衍射儀、紫外-可見分光光度計(jì)等測試手段對(duì)產(chǎn)物結(jié)構(gòu)和性能進(jìn)行了表征,研究了不同二氧化鈦質(zhì)量濃度、餌離子摻雜濃度對(duì)次甲基藍(lán)(MB)光催化性能的影響.結(jié)果表明,所制備的二氧化鈦的晶型為銳鈦礦型;餌離子摻雜的二氧化鈦對(duì)比純二氧化鈦的光催化性能有顯著提高.當(dāng)二氧化鈦質(zhì)量濃度為3 g/L時(shí),對(duì)MB的降解效果最好;通過研究餌離子摻雜對(duì)MB光催化動(dòng)力學(xué)模型,表明餌離子摻雜有較高的一級(jí)反應(yīng)速率Kapp,且餌離子最佳摻雜量為5%.

二氧化鈦;鉺摻雜;光催化;次甲基藍(lán)

印染企業(yè)在企業(yè)生產(chǎn)過程中將產(chǎn)生大量的工業(yè)廢水,如果將含有染料的工業(yè)廢水不加處理直接排放入河水湖泊中,將造成嚴(yán)重的染料污染.此類染料廢水具有以下幾個(gè)特點(diǎn):染料廢水濃度高、成分復(fù)雜、毒性大、污染物的種類比較多、易溶解、降解困難等[1].TiO2光催化降解廢水中污染物是一種新型的有關(guān)環(huán)境治理技術(shù),可以應(yīng)用于染料廢水、有機(jī)廢水、農(nóng)藥廢水、表面活性劑以及含油廢水等的降解,具有廣闊的前景[2].

本文采用水熱合成法制備了純TiO2以及餌摻雜TiO2光催化劑,通過對(duì)次甲基藍(lán)(MB)的降解實(shí)驗(yàn),結(jié)合XRD、UV-Vis表征分析結(jié)果,討論了TiO2的濃度、稀土Er3+摻雜量對(duì)MB光催化性能的影響,Er3+摻雜對(duì)MB光催化動(dòng)力學(xué)采用一級(jí)動(dòng)力學(xué)模型來描述[11],對(duì)比上述文獻(xiàn),本實(shí)驗(yàn)結(jié)果有較高的一級(jí)反應(yīng)速率Kapp,光催化時(shí)間較短.

1 實(shí)驗(yàn)部分

1.1 光催化劑的制備

按化學(xué)通式Ti1-xErxO2(x的取值范圍為0≤x≤0.1)稱取反應(yīng)試劑Er(NO3)3·5H2O、Ti(SO4)2并加入200 mL去離子水,在磁力攪拌器上進(jìn)行攪拌,邊攪拌邊加入20 mL氨水,攪拌30 min,待試劑完全溶解并混合均勻后用離心機(jī)進(jìn)行離心,取出沉淀物,把沉淀物轉(zhuǎn)移到錐形瓶中并加入200 mL去離子水和10 mL過氧化氫后進(jìn)行回流,回流4 h后將溶液放入反應(yīng)釜中,在180 ℃條件下加熱15 h.從反應(yīng)釜中取得樣品進(jìn)行離心,然后蒸發(fā)后得到Er3+摻雜的TiO2樣品.純TiO2制備方法同上,只是制備過程中不用添加Er(NO3)3·5H2O即可.

1.2 樣品的表征

Er3+摻雜的TiO2樣品的X射線衍射譜采用德國布魯克DX-2000型X射線衍射(XRD)儀測定,管電壓為40 kV,管電流40 mA,掃描范圍2θ=10°～80°,掃描步長為0.08°;MB的紫外-可見吸收光譜采用日本島津公司生產(chǎn)的UV3600型紫外-可見分光光度計(jì)(UV-vis)測定.

1.3 光催化性能研究

樣品的光催化性能以光催化降解MB來評(píng)價(jià).光源為250 W主波長365 nm的汞燈,光催化劑的加入量為2 g/L,加入200 mL質(zhì)量濃度為8 mg/L的MB溶液,調(diào)節(jié)pH后,在室溫條件下用磁力攪拌器攪拌,每隔10 min取10 mL反應(yīng)液,離心分離后取上層清液,用分光光度計(jì)(UV-vis)測定MB最大吸收波長為663 nm的吸光度值的變化可求得降解率η

(1)

其中:C0—樣品的溶液初始濃度,C—樣品的光催化一段時(shí)間的溶液濃度.

2 結(jié)果與分析

2.1 催化劑的表征

圖1為純TiO2和Er3+摻雜TiO2的XRD圖譜,其中(a)、(b)、(c)、(d)、(e)分別代表TiO2、Ti0.97Er0.03O2、Ti0.95Er0.05O2、Ti0.93Er0.07O2、Ti0.90Er0.10O2.從圖中可以看出,衍射峰曲線表明樣品晶型以銳鈦礦型為主,在衍射角2θ為25.3°處出現(xiàn)了很強(qiáng)的晶面衍射峰.衍射角在25.3°、37.8°、48.20°、53.9°、62.55°,分別對(duì)應(yīng)TiO2銳鈦礦型的(101)、(004)、(200)、(105)、(204)面衍射峰.圖中顯示制備的樣品結(jié)晶度較高,晶粒中基本沒有出現(xiàn)其它的雜質(zhì)峰,說明樣品的純度較高.從晶面衍射峰圖譜可以看出,隨著Er3+摻雜濃度的不斷增加,衍射角在25.3°對(duì)應(yīng)的(101)衍射峰強(qiáng)度減弱,從離子半徑角度來分析,由于Er3+半徑比Ti4+大,Er3+不易取代Ti4+從而進(jìn)入TiO2晶格內(nèi)部,而是以間隙取代的形式占據(jù)TiO2晶格的間隙位置,并且有一部分以稀土氧化物形式均勻分布在TiO2晶粒中,所以Er3+摻雜TiO2會(huì)使晶粒變小導(dǎo)致衍射峰強(qiáng)度逐漸減弱.

圖1 不同Er3+摻雜TiO2的XRD圖譜Figure 1 XRD spectra of TiO2 with different Er3+ contents

2.2 MB溶液的光催化降解機(jī)理和性能研究

圖2為MB的化學(xué)結(jié)構(gòu)和光催化反應(yīng)路徑,在光催化降解過程中MB中的色胺組含有N-脫烷基起著重要的作用[12],MB溶液的顏色逐漸減弱是由于部分甲基團(tuán)分解和藍(lán)移,最后MB溶液降解成H2O,CO2和其他無機(jī)分子[13].

圖2 MB的化學(xué)結(jié)構(gòu)和光催化反應(yīng)路徑Figure 2 Chemical structure of MB and the photocatalytic reaction pathway

TiO2+hv→e-+h+,

(2)

(3)

h++OH-→·OH,

(4)

(5)

圖3為MB溶液的吸光度A隨時(shí)間變化曲線,純TiO2光催化劑質(zhì)量濃度為3 g/L加入到200 mL質(zhì)量濃度為8 mg/L MB溶液,在光源為250 W主波長365 nm的汞燈照射120 min的條件下,在本實(shí)驗(yàn)中,有四個(gè)最大吸收峰分別在245 nm,292 nm,612 nm和663 nm.我們選擇研究發(fā)射帶為663 nm處的MB溶液濃度隨時(shí)間變化,光譜帶在663 nm發(fā)生藍(lán)移,如圖4藍(lán)移51 nm從663 nm到612 nm,最終隨著光催化降解消失,光譜帶在292 nm也發(fā)生藍(lán)移,從292 nm到285 nm,這與已有報(bào)道類似[15].

圖3 近紫外光下MB溶液的光譜隨時(shí)間變化曲線Figure 3 Temporal spectral changes of MB in aqueous TiO2 suspensions under UV illumination

圖4 光譜帶在663 nm處發(fā)生藍(lán)移量Figure 4 Wavelength blue-shifts of the 663 nm Spectra band

2.3 TiO2質(zhì)量濃度對(duì)MB光催化性能影響

如圖5,在光源為250 W主波長365 nm的汞燈照射80 min的條件下,TiO2光催化劑質(zhì)量濃度為1 g/L、2 g/L、3 g/L、4 g/L,加入到200 mL質(zhì)量濃度為8 mg/L MB溶液,當(dāng)純TiO2質(zhì)量濃度為3 g/L時(shí),MB的光催化降解率最大.當(dāng)繼續(xù)增加TiO2的用量,MB的光催化降解率不能繼續(xù)增加,反而下降,最佳降解質(zhì)量濃度為3 g/L.這是因?yàn)楣獯呋瘎┰黾?使催化表面積增加,提高光的利用率增加空穴和電子對(duì),來提高光催化降解率.當(dāng)光催化劑質(zhì)量濃度達(dá)到一定時(shí),可能形成聚集體,非輻射過程增加使光催化降解率降低.

在上述條件下,又增加了2組對(duì)照試驗(yàn),一組是只在汞燈照射下,另一組只添加純TiO2(3 g/L)沒有光照,80 min之后MB的光催化效率很低,基本無降解.說明MB只有同時(shí)在光照和添加催化劑的情況下才能有效地降解.

圖5 紫外光照射下MB的光催化降解 Figure 5 Photocatalytic degradation of MB under UV illumination

2.4 Er3+摻雜量對(duì)MB光催化的影響

利用紫外-可見分光光度計(jì)(UV-vis)對(duì)樣品光降解性能進(jìn)行表征.如圖6不同Er3+摻雜TiO2降解MB光催化效率,其光催化性能得到一定程度的提高,主要有以下幾個(gè)原因:

1)Er3+摻雜對(duì)TiO2晶格結(jié)構(gòu)的影響.因?yàn)镋r3+的半徑大于Ti4+的半徑,只有少量的Er3+進(jìn)入晶格內(nèi)部,取代了Ti4+.沒有進(jìn)入晶格內(nèi)部的Er3+以間隙取代的形式占據(jù)TiO2晶格的間隙位置,形成Ti—O—Er的鍵合.從光催化效率方面分析,Er3+進(jìn)入晶格內(nèi)部,取代了Ti4+,或是Er3+以間隙取代的形式都會(huì)使電荷不平衡,最終影響光催化效率[16].

2)Er3+摻雜對(duì)TiO2晶粒尺寸的影響.Er3+摻雜會(huì)使TiO2的晶粒尺寸減小,由于晶粒尺寸減小會(huì)導(dǎo)致晶粒內(nèi)部的內(nèi)應(yīng)力增加,從而改變TiO2的能帶結(jié)構(gòu),使能級(jí)與能級(jí)之間的間距變窄,最終影響光催化效率[17].

由圖6,當(dāng)催化時(shí)間為80 min時(shí),TiO2,Ti0.97Er0.03O2,Ti0.95Er0.05O2,Ti0.93Er0.07O2,Ti0.90Er0.10O2對(duì)應(yīng)的C/C0值依次為0.22,0.18,0.06,0.13,0.3,則Er3+的摻雜量為5%時(shí)光催化效率最高,此時(shí)的降解率為94%.Er3+摻雜量繼續(xù)增加,光催化性能反而降低.主要是因?yàn)閾饺脒^量的Er3+,Er3+會(huì)附著在TiO2的表面,會(huì)成為光生電子和空穴對(duì)的復(fù)合中心,增加了電子和空穴的復(fù)合幾率,使光催化性能下降.

圖6 不同Er3+摻雜TiO2降解MB隨時(shí)間變化曲線圖Figure 6 Photocatalytic degradation of MB with different Er3+ contents

2.5 Er3+摻雜對(duì)MB光催化動(dòng)力學(xué)研究

Er3+摻雜TiO2對(duì)MB溶液光催化降解過程,如圖7符合Langmuir-Hinshelwood速率方程[18]

(6)

其中:C—MB溶液光催化t時(shí)的質(zhì)量濃度值;k—速率常數(shù);K—吸附平衡常數(shù).

對(duì)速率方程(6)積分得到

lnC/C0=-Kappt.

(7)

其中:C0—MB溶液的初始質(zhì)量濃度,Kapp—一級(jí)反應(yīng)速率,t—反應(yīng)時(shí)間.

圖7 不同Er3+摻雜TiO2的降解動(dòng)力學(xué)Figure 7 Degradation kinetics of different Er-doped TiO2

Er3+摻雜對(duì)MB光催化動(dòng)力學(xué)采用一級(jí)動(dòng)力學(xué)模型來描述,如表1實(shí)驗(yàn)結(jié)果餌離子摻雜有較高的一級(jí)反應(yīng)速率Kapp,且餌離子最佳摻雜量為5%.

表1 MB降解動(dòng)力學(xué)常數(shù)和相關(guān)系數(shù)

Table 1 Degradation kinetics constants and correlation coefficient of MB

光催化劑 一級(jí)反應(yīng)速率/min-1相關(guān)系數(shù)TiO20.01830.9957Ti0.97Er0.03O20.02080.9990Ti0.95Er0.05O20.03330.9983Ti0.93Er0.07O20.02420.9966Ti0.9Er0.1O20.01440.9870

2.6 MB的降解效率比較

染料或有機(jī)化合物的降解效率高度依賴于實(shí)驗(yàn)條件,如光照射源、反應(yīng)時(shí)間、染料類型,以及使用的光催化劑[20].在這項(xiàng)研究中,我們比較了本研究與先前研究報(bào)告利用太陽光、高壓鈉燈、碘鎢燈、UV-LED燈作為光源對(duì)染料溶液進(jìn)行光催化降解,比較這些結(jié)果列于表2中.Er3+摻雜TiO2的具有較高的光催化性能主要是因?yàn)镋r-TiO2具有較為豐富的氧空位和表面缺陷,為俘獲電子和對(duì)污染物的吸附提供了很好的條件,加速了光生電子-空穴對(duì)的復(fù)合.另一方面汞燈源是一個(gè)很好的近紫外光源用于光催化降解染料.從上述比較的結(jié)果,Er3+摻雜TiO2是一個(gè)有效的光催化劑用于降解MB溶液.本文獲得Er3+摻雜TiO2的光催化時(shí)間為80 min時(shí),降解率達(dá)到94%.

表2 本文與已有文獻(xiàn)報(bào)道的降解率與降解時(shí)間對(duì)比

3 結(jié) 語

通過水熱合成法制備了TiO2和Er3+摻雜TiO2光催化劑,XRD圖譜表明所制備的二氧化鈦樣品結(jié)晶度較高,而且純度較高.通過制備Er3+摻雜TiO2對(duì)MB光催化性能的研究,Er3+的摻雜明顯提高了TiO2的光催化活性,有較高的一級(jí)反應(yīng)速率Kapp,最佳摻雜量為5%.其光催化時(shí)間為80 min時(shí),降解率達(dá)到94%,光催化效果優(yōu)異,具有較好的光催化處理染料廢水的前景.

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Preparation and photocatalytic performance of Er-doped TiO2

WEI Jian1,2, SHEN Changyu1, DAI Kai2

(1. College of Optical and Electronic Technology, China Jiliang University, Hangzhou 310018, China; 2. School of Physics and Electronic Information, Huaibei Normal University, Anhui Huaibei 235000, China)

The photocatalysts of TiO2and rare earth Er-doped TiO2were prepared by the hydrothermal synthesis method. The structure and the performance of the products were analyzed by using the X-ray diffraction (XRD) and ultraviolet-visible spectroscopy. We found that the crystal structure of TiO2was anatase, but the photocatalytic ability of Er-doped TiO2to methylene blue(MB) was improved significantly compared to the pure TiO2. The catalytic kinetics models of the catalysts to MB show that there is the highest reaction rateKappwith the concentration of TiO2at 3 g/L, while the optimal dosage of Er-doped is 5%.

TiO2; Er-doped; photocatalysis; methylene blue

1004-1540(2015)01-0080-07

10.3969/j.issn.1004-1540.2015.01.015

2014-07-18 《中國計(jì)量學(xué)院學(xué)報(bào)》網(wǎng)址：zgjl.cbpt.cnki.net

國家自然科學(xué)基金資助項(xiàng)目(No.61405185).

O643.3

A