Microwave-assisted Preparation Of Metal Phosphates And The Study Of Photocatalytic Performance

Three metal phosphate materials have been prepared by microwave-assisted heating method at low temperature under atmospheric pressure,including cobalt phosphate,copper hydroxylphosphate,and cobalt zirconium phosphate.The products were characterized by XRD,SEM,TEM,FT-IR,Raman,TG,DRS and SPV.These phosphates were used as heterogeneous catalysis to degrade printing and dyeing wastewater.The photocatalytic degradation performance of the phosphates were evaluated via a Fenton-like process,discussing the inner effects of morphology and preparation condition as well as the out effects of different H₂O2 dosage,different catalyst load,initial pH,initial dye concentration,different anions?i.e.Cl-?SO₄2-?NO3-?and calcined temperature on the degradation efficiency of wastewater.The photocatalytic mechanism of these metal phosphates were also studied in detail.1.Cobalt phosphate with different morphologies have been prepared via a microwave-assisted method.The morphology of cobalt phosphate prepared in the presence of hexamethylene tetramine?HMTA?is flower-like?fCoP?while the morphology is plate-like in the presence of urea?pCoP?.The fCoP and pCoP exhibited similar optical absorption properties;however,the SPV response intensity of fCoP was nearly eight times that of the plate-like one.The crystal growth behavior of f CoP follows an Ostwald ripening mechanism,the HMTA is the key template for the formation of flower-like hierachical structure.The performance of the photocatalytic degradation of Rhodamine B?RhB?via a Fenton-like process on cobalt phosphate with different morphologies was evaluated.The photocatalytic activity of fCoP was considerably higher than the plate-like one.The degradation efficiency of RhB was influenced by the load of fCoP and the dosage of H₂O2.The addition of anions in the solution or calcination of fCoP can both decrease the photocatalytic activities of fCoP.Besides,fCoP can overcome the drawback of a narrow pH range of homogeneous Fenton reaction and keep high catalytic activities over a wider pH range.Additionally,fCoP possessed excellent durability and structural stability with consecutive runs.The research on the photocatalytic mechanism showed that the synergistic effect between the Fenton-like reaction and photocatalysis maybe both lead to the remarkable catalytic performance in heterogeneous Fenton-like process.The catalytic activation was confirmed to be related to both the Co?II?on the surface and the cobalt phosphate framework.2.Copper hydroxyphosphate?Cu₂?OH?PO₄?was synthesized by microwave-assisted method at low temperature under atmosphere pressure.The morphologies of Cu₂?OH?PO₄ would be urchin-like,grain-like and prism when using different initial concentrations and surfactants.Compared with the hydrothermal methods,the new method is environmental friendly for the using of phosphate at the stoichiometric ratio which increase the utilization rate of raw materials and decrease the phosphorus emissions.Furthermore,the reaction time has been shortened from three days to thirty minutes which reduced the energy consumption.Most of important,using urea instead of ethylenediamine which would also reduce the poison to the human body.The performance of the photocatalytic degradation of methylene blue?MB?via a Fenton-like process on Cu₂?OH?PO₄,discussing the effects of different preparation condition on catalytic performance.The photocatalytic activity of grain-like Cu₂?OH?PO₄ was considerably higher than the urchin-like and prism one.The degradation efficiency of MB was influenced by the load of Cu₂?OH?PO₄ and the dosage of H₂O2.The addition of anions in the solution had little effect on the photocatalytic activity of Cu₂?OH?PO₄.Besides,Cu₂?OH?PO₄ can overcome the drawback of a narrow pH range of homogeneous Fenton reaction and keep high catalytic activities over a wider pH range.Additionally,Cu₂?OH?PO₄ possessed excellent durability and structural stability with consecutive runs.The research on the photocatalytic mechanism showed that the synergistic effect between the Fenton-like reaction and photocatalysis maybe both lead to the remarkable catalytic performance in heterogeneous Fenton-like process.The catalytic activation was confirmed to be related to both the Cu?II?and P-OH on the surface.3.Coil-like cobalt zirconium phosphate microspheres?CoZr?PO₄?2·4H₂O,CZP?were prepared via the microwave-assisted method in an open system.There are large influence on the morphology of CZP with different molar ratio of [F-]/[Zr⁴⁺] and [PO₄^3-]/[Zr⁴⁺].The best molar ratio of [F-]/[Zr⁴⁺] is 6 and the appropriate molar ratio of [PO₄^3-]/[Zr⁴⁺] is 20.The crystal growth behavior of coil-like CZP follows an Ostwald ripening mechanism,the presence of Co2+ can induce the hexagonal plates self-assemble from 2D structure to 3D hierarchical structure.The photodegradation of MB under UV light irradiation was carried to evaluate the photocatalytic performance of CZP.It was observed that coil-like CZP possessed good durability and structural stability after five runs.The study of the photocatalytic degradation mechanism showed that HO· is the main active species in the photocatalytic process.The CZP can also be used as microwave absorber;however,the microwave absorbing ability is limited.The low impedance matching is the main reason for the limited reflection loss.