Investigation on photocatalytic characteristics of Ag-TiO2-graphene and Ag3PO4-TiO2-graphene oxide ternary nanocomposite photocatalysts

[[abstract]]本研究利用光催化還原法製備銀/二氧化鈦/石墨烯(ATG)及離子交換法製備磷酸銀/二氧化鈦/氧化石墨烯(APTGO)三元奈米複合物光觸媒。我們分別調整ATG中石墨烯和銀的含量，也調整了APTGO中磷酸銀和二氧化鈦的莫耳比，並進行材料特性、光催化活性分析，以及光降解機制之探討。 當ATG中石墨烯越多，可見光吸收增加，電荷傳輸效率提高，有利於光降解和水分解產氫。ATG中二氧化鈦和石墨烯之最佳混合比例為5:1。當銀越多，可見光吸收也增加，界面阻抗降低，導電性提高，且銀奈米粒子引起的表面增強拉曼散射效應亦有助於提升光催化活性。然而，過量的銀減少光觸媒之比表面積，反而造成光吸收降低、再結合機率增加，因此適量的銀才能更有效地提升光催化活性。不同二氧化鈦和石墨烯的混合比例下有不同的最佳銀含量，當最佳石墨烯與銀含量存在時，ATG才有最佳光催化效率，達最大產氫量4233 mole g-1，量子效率為26.2 %；此外，利用光催化還原法可以有效縮短ATG的製備時間，相較於水熱法的製備時間縮短4至22小時。 APTGO中二氧化鈦增加可提高光吸收，但同時也造成界面阻抗越大，電荷傳輸性質變差，且過量的二氧化鈦覆蓋於磷酸銀和氧化石墨烯表面會減少光觸媒之比表面積，降低整體光吸收度。適量的二氧化鈦才有利於提升光催化性能。實驗結果證明當APTGO中磷酸銀和二氧化鈦之莫耳比為0.6時有最佳二氧化鈦含量，此時光吸收度最大、光吸收範圍最廣，可得到最大產氫量1312 mole g-1，量子效率為8.13 %。[[abstract]]In this study, photocatalytic reduction and ion exchange methods were employed to fabricate the ternary nanocomposite photocatalysts of Ag-TiO2-graphene (ATG) and Ag3PO4-TiO2-graphene oxide (APTGO), respectively. The contents of graphene and Ag in ATG were adjusted, and the molar ratio of Ag3PO4 to TiO2 in APTGO was tuned. The properties and photocatalytic activity of the nanocomposites were examined, and their photodegradation mechanisms were explored. When an ATG had more graphene, light absorption and charge transport were enhanced, leading to higher efficiencies of photodegradation and hydrogen production from water splitting. It was proved that the optimum ratio between TiO2 and graphene was 5:1. More Ag contributed to light absorption and reduced impedance. The surface enhanced Raman scattering (SERS) effect induced by Ag nanoparticles was favorable to photocatalytic activity. However, excess Ag decreased the specific surfacearea of an ATG photocatalyst, and lower light absorption and increased recombination probability were thereby caused. Accordingly, an appropriate content of Ag was required so as to obtain more effective photocatalysis. Moreover, it was found that the optimum Ag content was different for a different mixing ratio between TiO2 and graphene. The best photocatalytic efficiency of ATG (max. hydrogen production 4233 mole g-1 and QE = 26.2 %) was achieved when graphene and Ag both existed optimal contens. More TiO2 in APTGO improved light absorption but caused a larger impedance and inferior charge transport. Excess TiO2 distributed over the surfaces of Ag3PO4 and graphene oxide decreased the specific surface area and thus lower light absorbance of an APTGO photocatalyst. It has been evidenced that an appropriate TiO2 content was beneficial to enhance photocatalytic performance. Larger and wider light absorption and thereby highest photocatalytic efficiency of APTGO (max. hydrogen production 1312 mole g-1 and QE = 8.13 %) were achieved when the molar ratio of Ag3PO4 to TiO2 was 0.6.[[note]]碩