Preparation of coal gangue/BiVO4 composite photocatalyst and its degradation of xanthate wastewater
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摘要: 选矿废水中的黄药会严重危害环境,钒酸铋能在可见光条件下实现黄药的降解,但其严重的电子-空穴复合影响其实用性,鉴于煤矸石丰富的孔隙结构及成分组成,本文采用水热法合成了煤矸石负载型光催化剂(CG/BiVO4),运用XRD、FTIR、SEM、UV-Vis DRS、PL等手段对催化剂进行表征,以黄药为目标污染物,在可见光作用下考察黄药的光催化降解性能及煤矸石改性钒酸铋的作用机制。结果表明,与纯BiVO4相比,负载型CG/BiVO4的光催化性能显著提高,在煤矸石负载量20wt%,pH=7、催化剂投加量为1.5 g/L、黄药初始浓度C0=10 mg/L的条件下,CG/BiVO4在540 min时对黄药的降解率达到最大,为93%,黄药的光降解过程符合一级动力学模型,处理后化学需氧量浓度CCOD为11.47 mg/L,符合排放标准要求。响应面分析得到的最优反应条件下的预测值与实际降解率仅相差0.96%,可见该模型可较好地预测20%-CG/BiVO4对黄药废水的降解率。结合各项表征分析可知,CG的负载可显著增加催化剂的比表面积,提高其对可见光的响应,改善光催化体系中电子和空穴的分离效率的同时降低光生电子-空穴对复合几率,这是复合光催化剂性能提高的重要原因;机制分析得知,黄药光降解的主要自由基为h+,•O2− 和•OH次之,黄药中的烷基、C=S在自由基作用下首先发生断裂,形成中间产物过黄药(ROCSSO−),随后矿化生成SO42−等小分子,光反应7 h,S的转化率与黄药降解率接近,且循环5次,降解率不低于90%,可见该催化剂具有较好的光催化性能,这为煤矸石在光催化领域的资源化利用奠定了理论基础。Abstract: Xanthate in mineral processing wastewater can do serious harm to environment. Bismuth vanadate can degrade xanthate under visible light, but its serious electron-hole complex affects its practicability, in view of the abundant pore structure and composition of coal gangue, the coal gangue supported photocatalyst (CG/BiVO4) was synthesized by hydrothermal method. The catalysts were characterized by XRD, FTIR, SEM, UV-Vis DRS, PL, the photocatalytic degradation of xanthate and the mechanism of coal gangue modified bismuth vanadate were investigated under visible light. The results showed that the photocatalytic activity of the supported CG/BiVO4 is significantly higher than that of the pure BiVO4. Under the conditions of 20wt% coal gangue loading, pH=7, catalyst dosage is 1.5 g/L, initial concentration of xanthate C0=10 mg/L, the degradation rate of xanthate over CG/BiVO4 reached the maximum at 540 min, which was 93% . The photodegradation process of xanthate complied with the first-order kinetic model. After treatment, the concentration of chemical oxygen demand CCOD was 11.47 mg/L, which met the emission standard. The predicted degradation rate of 20%-CG/BiVO4 was only 0.96% different from the actual degradation rate, which indicated that the model could predict the degradation rate of 20%-CG/BiVO4. The results show that the loading of CG can significantly increase the specific surface area of the catalyst, improve its response to visible light, increase the separation efficiency of electrons and holes in the photocatalytic system, and decrease the recombination probability of photogenerated electrons and holes, this is an important reason for the improvement of the performance of the composite photocatalyst, the mechanism analysis showed that h+ was the main free radical in xanthate photodegradation, while •O2 − and •OH were secondary, under the action of free radical, the alkyl group and C=S in the xanthate were firstly broken, and formed the intermediate product, peroxy xanthate (ROCSSO−) , then mineralized to form small molecules such as SO42−. After 7 h of photoreaction, the conversion of Sulfur was close to the degradation rate of xanthate, and the degradation rate was not less than 90% after 5 cycles, it can be seen that the catalyst has good photocatalytic performance, which lays a theoretical foundation for the resource utilization of coal gangue in the photocatalytic field.
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Key words:
- coal gangue /
- BiVO4 /
- photocatalysis /
- xanthate /
- visible light /
- degradation /
- wastewater
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图 8 (a) CG、BiVO4与CG/BiVO4对黄药的吸附平衡图;(b) CG、BiVO4与CG/BiVO4对黄药的降解效果图;(c) 一级动力学模型
Figure 8. (a) Adsorption equilibrium diagram of CG, BiVO4 and CG/BiVO4 composite on xanthate; (b) Degradation effect of CG, BiVO4 and CG/BiVO4 composite on xanthate; (c) The first-order kinetic model
k—First-order kinetics constant; C0—Initial concentration of xanthate solution (25 mg/L); C—Xanthate concentration in solution
表 1 BiVO4与煤矸石(CG)/BiVO4的命名与比表面积
Table 1. Naming and specific surface area of BiVO4 and coal gangue (CG)/BiVO4
Sample Specific surface area/(m2∙g−1) Mass fraction of CG/wt% BiVO4 2.5 — 5%-CG/BiVO4 7.5 5 10%-CG/BiVO4 8.0 10 20%-CG/BiVO4 8.2 20 30%-CG/BiVO4 8.7 30 表 2 影响CG/BiVO4光降解黄药的因素及水平
Table 2. Factors and levels affecting CG/BiVO4 photodegradation of xanthate
Factor Lever −1 0 +1 pH 7 9 11 Dosage of catalyst/(g∙L−1) 3 3.5 4 C0/(mg∙L−1) 10 25 50 Note: C0—Xanthate initial concentration. 表 3 优化CG/BiVO4光降解黄药实验中回归模型的方差分析1
Table 3. Variance analysis of regression model 1 in optimizing CG/BiVO4 photodegradation of xanthate
Source SS DF Mean square F value p value prob>F Coefficient Model 118.69 9 13.19 49.93 <0.0001 Significant A 43.88 1 43.88 166.11 <0.0001 −2.38 B 0.26 1 0.26 1.00 0.3505 −0.18 C 32.36 1 32.36 122.52 <0.0001 −2.01 AB 0.56 1 0.56 2.13 0.1878 0.37 AC 14.63 1 14.63 55.37 0.0001 1.88 BC 0.36 1 0.36 1.35 0.2830 0.29 A2 12.23 1 12.23 46.30 0.0003 1.70 B2 2.77 1 2.77 10.50 0.0142 0.81 C2 1.19 1 1.19 4.49 0.0718 0.58 Residual 1.85 7 0.26 Lack of fit 1.30 3 0.43 3.19 0.1460 Not significant Pure error 0.55 4 0.14 Cor total 120.54 16 Notes: A—Initial pH of the reaction; B—Catalyst dosage; C—Initial concentration of xanthate; SS—Sum of squares; DF—Degree of freedom. 表 4 优化CG/BiVO4光降解黄药实验中回归模型的方差分析2
Table 4. Variance analysis of regression model 2 in optimizing CG/BiVO4 photodegradation of xanthate
Project Value Project Value Std.Dev 0.51 R2 0.9847 Mean 87.49 Adj R-Squared 0.9649 CV/% 0.59 Pred R-Squared 0.8166 PRESS 22.10 Adeq precisior 23.555 Notes: Std.Dev—Standard deviation; CV—Coefficient of variation; PRESS—Predicted residual error sum of square; R2—Coefficient of determination; Adj—Adjusted multiple correlation cofficient; Pred—Predictive correlation coefficient; Adeq—Adeq precision. 表 5 CG/BiVO4光降解黄药过程中的SO42−浓度与S转化率
Table 5. SO42− concentration and sulfur conversion in photodegradation of xanthate by CG/BiVO4
Light time/h Concentration of
SO42−/(mg·L−1)Conversion of
sulfur/%1 12.86 25.72 2 22.25 44.50 3 27.48 54.96 4 28.75 57.50 5 31.29 62.58 6 38.24 76.48 7 45.34 90.68 -
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