Facile synthesis of Ag3PO4/g-C3N4 composites in various solvent systems with tuned morphologies and their efficient photocatalytic activity for multi-dye degradation

Synthesis of a stable and efficient photocatalyst has been a key research goal in recent years. Silver phosphate/carbon nitride (APO/CN) composites have been recognized as an effective photocatalyst to degrade organic dye pollutants using solar energy. The aim of this work is to study the effect of the solvents on the structural and physical properties of APO/CN to enhance their photostability and photocatalytic activity through light absorption, charge separation, tuning morphology and surface reactions. APO/CN-composites with various CN mass loading were first synthesized via an in-situ wet chemical method to find the optimum CN loading. APO/CN (25 wt%) was observed to exhibit superior photocatalytic activity for dye degradation, therefore, it was selected for further studies. APO/CN-25 wt% was prepared in three different solvent systems: Deionized water (DJ water), tetrahydrofuran (THF), and ethylene glycol (EG) to make APO/CN-25 wt%-solvent composites. FE-SEM and TEM were used to characterize their morphologies, while their photocatalytic activity and stability were investigated by rhodamine b (RhB), methylene blue (MB) and 4-nitrophenol (NP) degradation studies. UV-Vis spectrophotometer was used to monitor changes in dye concentration. In D.I water, CN nanosheets are decorated on orthorhombic APO microstructures; while in EG, the orthorhombic structures of APO microstructure are transformed into tetrapod microstructures with CN nanosheets sparsely decorated on their surfaces. In contrast, a uniform wrapping of CN nanosheets on the orthorhombic structure APO microstructure was observed in THF. Outstanding photocatalytic activity was observed for the APO/CN-25 wt%-THF material: its dye degradation rate is 3.69 and 1.17 times that of APO/CN-25 wt%-D.I water; 1.43 and 1.58 times that of APO/CN-25%-EG for RhB and MB, respectively. This is due to the uniform wrapping of CN nanosheets on the APO microstructure in APO/CN-25 wt%-THF which led to intimate contact between the heterojunction and efficient charge separation. The photocatalytic efficiency of APO/CN-25 wt%-solvent follows the order of THF > EG > D.I. water. APO/CN-25 wt%-THF retains almost the same catalytic activity after 3 recycles runs which is a clear indication of its stability. Overall, the superior photocatalytic efficiency of the APO/CN composites is due to the co-catalytic influence of CN and APO which offer enhanced charge separation within the heterojunction interface. THF helps to fabricate APO/CN composites with a morphology which ultimately accelerate the photocatalysis process.