BiYO₃:Preparation, Modification, And Its Application In Photocatalytic Reduction Of Carbon Dioxide

With the rapid development of industry, coal, oil, natural gas and other hydrocarbon fuels continue to be consumed, the emissions of carbon dioxide are increasing in the atmosphere. Global warming is an increasingly serious situation and becoming a global environmental problem which affecting humanity.In this paper, BiYO₃ catalyst were prepared by a hydrothermal method and the modification of Cu was adopted. The microstructure of BiYO₃ catalyst and the photocatalytic reduction of CO₂ conversion to HCOOH was investigated. The following three aspects were included in the studies:Firstly, BiYO₃ were prepared by a hydrothermal method using the sodium dodecyl benzene sulfonate（SDBS）, disodium ethylenediamine tetraacetate （EDTA）, and citric acid（CA） as the soft template. Characterized the catalysts and the effects of templates on the formed BiYO₃ nanostructures were revealed. The results show, The BiYO₃ nanostructures prepared without template and with the existence of SDBS, EDTA, and CA templates were flake, slice, rectangular lath with fine particles, and scaly uniform particles. The photocatalytic reduction of CO₂ under visible-light irradiation with these synthesized BiYO₃ nanostructures was studied and compared. Due to the greater specific surface area (20.87 m2·g^-1), higher adsorbed edge （569 nm）, and lower band gap （2.18 eV）, which could absorb more visible light to react. BiYO₃ prepared by using EDTA as template produced fewer hydroxyl free radicals （·OH） to give a higher yield of formic acid （HCOOH） in the process of photocatalytic reduction of CO₂. The HCOOH yield from the photocatalytic reduction of CO₂ by EDTA synthesized BiYO₃ was 1.68 μmol·mL^-1,1.9 times higher than 0.90 μmol·mL^-1 of the BiYO₃ nanocatalysts prepared without template, and 2.6 times higher than 0.64 μmol·mL^-1 of the BiYO₃ prepared by a solid-state reaction.Secondly, the photocatalyst is BiYO₃-EDTA and the effects of reaction time, catalyst amount, flow rate of carbon dioxide, reductant specieson, on the photocatalytic reduce of CO₂ conversion, repeated use of BiYO₃ and reaction mechanism were studied. The results show that the optimum technological conditions for photocatalytic reduction of CO₂ were:reaction time was 6 h, flow rate of CO₂ was 100 mL·min^-1, catalyst amount was 0.40 g, reductant concentration was 0.25 mol·L^-1 NaOH and 0.10 mol·L^-1 Na2SO₃. Under the optimum conditions, the yield of HCOOH was 1.68 μmol·mL^-1. And when the photocatalyst reused six times, the HCOOH yield (1.57 μmol·mL^-1) was reduced by 6.5%, which showed that the catalyst could still maintain a good activity stability after six times of repeated utilization.Finally, Cu/BiYO₃ photocatalysts with different Cu contents of 0.5%,1.0%, 2.0% and 3.0% （mole fraction） were prepared by a hydrothermal method. The effect of different Cu doping amount on the structure of BiYO₃ catalyst the photocatalytic reduction of CO₂ under visible-light irradiation were investigated to find out the best doping amount of Cu. Research results show that, Cu-doped had an advantage on improving the photocatalytic activity of BiYO₃. BiYO₃ with Cu doping content of 2% showed the greater specific surface area (18.64 m2·g^-1), higher adsorbed edge （549 nm）, and lower band gap （2.26 eV）, a higher yield of HCOOH in the process of photocatalytic reduction of CO₂, which caused by the lower property for produced·OH. The yield of HCOOH of photocatalytic reduction of CO₂ was 2.04 μmol·mL^-1, which was 2.2 times higher than BiYO₃ prepared with undoped Cu, and 2.7 times higher than that of Degussa P25. The optimum doping content of Cu was 2%.The effects of reaction time, catalyst amount, flow rate of carbon dioxide, reductant specieson on the photocatalytic reduce of CO₂ conversion and repeated use of catalyst were studied by 2% Cu/BiYO₃. The results show that the optimum technological conditions for photocatalytic reduction of CO₂ were:reaction time is 6 h, flow rate of CO₂ is 120 mL·min^-1, catalyst amount is 0.50 g, reductant concentration is 0.20 mol·L^-1 NaOH and 0.12 mol·L^-1 Na2SO₃. Under the optimum conditions, the yield of HCOOH was 2.04 μmol·mL^-1. And when the photocatalyst reused five times, the HCOOH yield (1.90 μmol·mL^-1) was reduced by 7.2%, which showed that the catalyst could still maintain a good photocatalytic activity after five times of repeated utilization. The photocatalyst is 2% Cu/BiYO₃ and the effects of reaction time, catalyst amount, flow rate of carbon dioxide, reductant specieson, on the photocatalytic reduce of CO₂ conversion and repeated use of BiYO₃ were studied.