An efficient strategy for photocatalytic hydrogen peroxide production over oxygen-enriched graphitic carbon nitride with sodium phosphate

富氧石墨相氮化碳在磷酸钠溶液中高效光催化合成过氧化氢

Photocatalytic hydrogen peroxide(H_(2)O_(2))production is a promising strategy to replace the traditional production processes;however,the inefficient H_(2)O_(2) productivity limits its application.In this study,oxygen-rich g-C_(3)N_(4) with abundant nitrogen vacancies(OCN)was synthesized for photocatalytic H_(2)O_(2) production.X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy indicated that oxygen-containing functional groups(–COOH and C–O–C)were obtained.Electron paramagnetic resonance confirmed the successful introduction of nitrogen vacancies.OCN exhibited efficient photocatalytic H_(2)O_(2) production performance of 1965μmol L^(−1) h^(−1) in air under visible-light irradiation.The high H_(2)O_(2) production was attributed to the enhanced adsorption of oxygen,enlarged specific surface area,and promoted carrier separation.An increased H_(2)O_(2) production rate(5781μmol L^(−1) h^(−1))was achieved in a Na_(3)PO_(4) solution.The improved performance was attributed to the changed reactive oxygen species.Specifically,the adsorbed PO_(4)^(3−) on the surface of the OCN promoted the transfer of holes to the catalyst surface.•O_(2)−obtained by O_(2) reduction reacted with adjacent holes to generate 1O_(2),which could efficiently generate H_(2)O_(2) with isopropanol.Additionally,PO_(4)^(3−),as a stabilizer,inhibited the decomposition of H_(2)O_(2).

过氧化氢是一种重要的化工原料,广泛应用于杀菌、漂白、燃料电池、化工生产、环境修复等领域.目前工业生产过氧化氢以蒽醌法为主,但多步蒽醌氧化工艺存在能耗高和污染环境等不足.因此,急需开发一种低能耗且环境友好的过氧化氢合成工艺.光催化是一种理想的过氧化氢合成方法,该方法以太阳光作为能源,水或氧气作为原料,在绿色、温和的条件下实现过氧化氢的生产.本文制备了一种含有氮空位的富氧石墨相氮化碳(OCN),并考察了其光催化生产过氧化氢的性能.以空气中的氧气为原料,OCN光催化剂在可见光照射下高效合成了过氧化氢,产率为1965μmol L^(−1) h^(−1).通过将磷酸钠引入反应体系,进一步提高了过氧化氢的产率,产率最高可达5781μmol L^(−1) h^(−1).本文在光催化性能测试的基础上,还通过一系列表征手段研究了OCN高效生产过氧化氢的机理.X射线光电子能谱和傅里叶红外光谱研究表明,OCN表面存在含氧官能团(–COOH和C–O–C).电子顺磁共振谱证明OCN中含有大量的氮空位.氧气程序升温脱附、透射电子显微镜、氮气等温吸附脱附曲线、稳态荧光光谱和电化学分析结果表明,OCN较好的光催化性能归因于氧气吸附能力增强、片层结构减小、比表面积增大以及载流子分离效率提高.过氧化氢产率的进一步提高归因于反应体系中活性氧物种的改变,本文通过EPR测试验证了在不同反应条件下反应体系中产生的活性氧物种,并提出可能的反应机理:含氧官能团作为光催化反应的活性位点促进了OCN表面对氧气的吸附和活化,可见光激发下OCN产生光生电子和空穴,光生电子将OCN表面吸附的氧气还原为超氧自由基;带负电的磷酸根吸附在OCN的表面,通过静电吸引力促进光生空穴向催化剂表面迁移,迁移到OCN表面的光生空穴与相邻的超氧自由基反应产生单线态氧;单线态氧与异丙醇快速反应得到产物过氧化氢.此外,磷酸根作为稳定剂能够抑制H_(2)O_(2)分解.综上,本文设计了一种用于高效合成过氧化氢的光催化剂,并为光催化过氧化氢合成的反应路径提供了新的理解和认识.