近年发展起来的低能耗、高效率的光催化技术为解决环境污染和能源短缺等问题提供了新途径. 在众多光催化材料中, 非金属石墨相氮化碳(g-C3N4)半导体材料因其化学稳定性和热稳定性优异、能带结构易调控、前驱体价格低廉等特点备受关注. 然而, g-C3N4的光生电子-空穴对极易复合, 比表面积较小, 不能充分利用太阳光等, 因而其光催化活性较低. 目前, 为了提高g-C3N4光催化性能, 多采用金属或非金属元素掺杂、与其他物质形成异质结、与其他半导体材料进行共聚合等方式. 其中, 共聚合有利于调节g-C3N4内部电子结构, 促进g-C3N4光生载流子的分离与迁移, 而且具有高度离域π-π*共轭结构的导电聚合物更适合与g-C3N4进行共聚合, 从而进一步提高g-C3N4的光催化性能.本文采用原位聚合法制备合成了导电聚吡咯(PPy)与g-C3N4的复合材料, 并以10 mg L-1亚甲基蓝(MB)作为目标污染物评价其可见光催化性能. 经X射线衍射、扫描电镜、透射电镜、比表面积、紫外-可见光谱等一系列表征分析可知, PPy/g-C3N4复合物(002)晶面衍射峰强度较g-C3N4减弱, 表明PPy抑制了g-C3N4晶型生长, 但未影响其晶型结构. 不规则薄片状g-C3N4表面均匀地负载有非晶态PPy颗粒, 复合物微观形貌发生变化. PPy与g-C3N4共轭芳香环层间堆积形成的介孔、大孔孔径和孔容积均增加, 比表面积增大了7 m2g-1, 使目标污染物能与光催化剂表面活性物质充分接触反应. 同时, PPy具有较强吸光系数, 对可见光能完全吸收; PPy/g-C3N4复合物的可见光吸收边带发生红移, 呈现出较g-C3N4更强的可见光吸收能力, 提高对可见光的利用效率.光催化降解MB实验结果表明, 在可见光(12 W LED灯)照射2 h后, 含有0.75 wt% PPy的复合样品0.75PPy/g-C3N4表现出最佳光催化活性, MB降解效率为99%; 且污染物光催化降解过程符合准一级动力学, 反应速率常数(0.03773 min-1)约为同条件下g-C3N4(0.01284 min-1)的3倍. 自由基捕获测试实验表明, g-C3N4和0.75PPy/g-C3N4均产生了·O2-自由基, 但后者的·O2-信号更强. 这是因为PPy也可吸收可见光并激发出电子, 该电子转移到g-C3N4导带, 再与其本身的电子共同与O2反应生成·O2-. 然而只有0.75PPy/g-C3N4在光催化过程中产生了·OH自由基, 是由于g-C3N4的价带(+1.4 eV)较H2O/·OH(+2.38 eV vs. NHE)和OH-/·OH(+1.99 eV vs.NHE)小,此价带上的h+不能与H2O和OH-反应生成·OH,而是由生成的·O2-再与e-和H+反应产生, 即·O2-+ 2H + 2e-CB→ ·OH + OH-. 本文最后分析了以·O2-和·OH作为主要活性物质的PPy/g-C3N4复合物光催化降解污染物的反应机理, PPy具有强导电性, 可作为光生电子和空穴的传输通道, 抑制其在g-C3N4表面的复合.%Polypyrrole-modified graphitic carbon nitride composites (PPy/g-C3N4) are fabricated using an in-situ polymerization method to improve the visible light photocatalytic activity of g-C3N4. The PPy/g-C3N4is applied to the photocatalytic degradation of methylene blue (MB) under visible light irradiation. Various characterization techniques are employed to investigate the relationship be-tween the structural properties and photoactivities of the as-prepared composites. Results show that the specific surface area of the PPy/g-C3N4composites increases upon assembly of the amor-phous PPy nanoparticles on the g-C3N4surface. Owing to the strong conductivity, the PPy can be used as a transition channel for electrons to move onto the g-C3N4surface, thus inhibiting the re-combination of photogenerated carriers of g-C3N4and improving the photocatalytic performance. The elevated light adsorption of PPy/g-C3N4composites is attributed to the strong absorption coef-ficient of PPy. The composite containing 0.75 wt% PPy exhibits a photocatalytic efficiency that is 3 times higher than that of g-C3N4in 2 h. Moreover, the degradation kinetics follow a pseu-do-first-order model. A detailed photocatalytic mechanism is proposed with ·OH and ·O2- radicals as the main reactive species. The present work provides new insights into the mechanistic under-standing of PPy in PPy/g-C3N4composites for environmental applications.
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