Preparation Of TiO₂ Nanosheets Modified With Sulfuric Acid And Its Performance In The Photocatalytic Reduction Of CO₂ Under Visible Light Irradiation

Nowadays, "global warming" and "carbon energy crisis" have become the major environmental problems and threat affecting human survival and development. The use of photocatalytic technology to reduction of CO₂ into hydrocarbon fuels has scientific significance and application value, which can not only mitigate the atmospheric level of CO₂, but also effectively store solar energy in the form of chemical bonds?mainly C-H?. However, there are some problems with titanium dioxide, such as wide band gap and low quantum efficiency, which greatly restricts its wide application. To extend the photoresponse region of TiO₂ and develop visible-light-induced TiO₂ with high photocatalytic activity is the inevitable trend for photocatalytic development into practical application. The paper aims to synthesize sulfate-modified TiO₂ nanosheet catalysts with high visible light activity for photocatalytic reduction of CO₂ under visible light irradiation. The main contents are given as follows: A series of {001} facets dominated TiO₂ nanosheets modified with sulfuric acid have been synthesized through hydrothermal treatment at 240 oC followed by acidification-heat treatment. The resultant catalyst powders were characterized by X-ray diffractometry?XRD?, field-emission scanning electron microscopy?FESEM?, transmission electron microscopy?TEM?, X-ray photoelectron spectroscopy?XPS?, electron paramagnetic resonance?EPR?, UV-vis diffuse reflectance spectroscopy?UV-vis DRS?, Raman spectroscopy, photoluminescence?PL? spectra, and Brunauer-Emmett-Teller?BET? N2 adsorption to probe the significant dependence of catalytic activity on physicochemical properties of the catalysts. The photocatalytic activity of the prepared catalysts was evaluated by the photocatalytic conversion of CO₂ with water vapor to CH₄ under visible-light irradiation. Experimental results show that:?1? Compared with untreated TiO₂ nanosheets, the H₂SO₄-modified samples exhibited markedly improved yield, quantum yield?QY?, energy returned on energy invested?EROEI?, and turnover number?TON? for CO₂ reduction to CH₄ under visible-light irradiation. The photocatalytic activity of TiO₂ nanosheets in the reduction of CO₂ under visible light irradiation is obviously enhanced after H₂SO₄ acidification treatment. The enhanced photocatalytic performance can be attributed to acidification promoting the formation of hydroxyl groups and oxygen vacancies/Ti3+ species as well as prolonging lifetime of photogenerated electron-hole pairs. Thus, efficient charge separation and transfer to the TiO₂ surface for both CO₂ reduction and the accompanying H₂ O oxidation is facilitated.?2? The optimal photocatalyst was found to be that treated with 0.5 mol L-1 H₂SO₄. After 4 h of reaction, the CH₄ yield was 13.20?mol g-1, corresponding to a QY, EROEI, and TON of 0.726‰, 0.335‰, and 83.124, respectively.?3? The catalyst maintained stable performance throughout five successive recyclability test runs. The research, with significant academic value and potential application, will not only provide an innovative approach for the design and preparation of new photocatalytic materials, but also could be extended to applications in removing other types of chemicals in the atmosphere.