STEP Organic Synthesis:Solar Photo-Electro-Thermal Chemistry Driven For Efficient Synthesis Of Benzoic Acid

Solar energy is widely used and concerned as a sustainable green energy.It has made a significant progress in the application of solar energy in the solar water heater,solar cell and so on.However,the use of solar energy technology in the past is based on the single mode with only partial solar energy is used.Therefore,the utilization efficiency of solar energy is limited.In order to improve the comprehensive utilization efficiency of solar energy,and making a breakthrough at the bottleneck of direct electrolysis for benzoic acid synthesis,the solar thermal-electrical coupling model for organic electrochemical synthesis is proposed.To determine whether the oxidation reaction of toluene can be processed,the calculation and analysis of thermodynamics theory are carried out.The reaction conditions of one-step direct solar thermal-electrical coupled oxidation of toluene to benzoic acid are optimized.The effects of different anode materials and their surface functionalization of anodes on the product composition and reactive selectivity for the oxidation of toluene are studied.In addition,an innovative idea for oxidation of toluene to benzoic acid by electrochemical synthesis through solar thermal field,electric field and its photocatalytic coupling method is proposed.Based on the new anode of TiO₂ nanotubes,the solar thermal-electrical-photo coupled fields are established.The mechanisms of one step oxidation of toluene to benzoic acid under the three coupled fields are revealed.The studies pave the way for efficient use of solar energy.The main contents are as follows:?1?Solar STEP organic synthesis model was proposed and set up.Theoretical analysis of thermodynamic analysis and chemical reaction are carried out.Results indicate that STEP solar thermoelectric coupling model can be used for the synthesis of benzoic acid due to the reaction of benzoic acid from toluene oxidation is endothermic process.?2?By using of chemical inert platinum anode,benzoic acid was synthesized by oxidation of toluene by means of STEP solar thermal electric coupling model.First,we determined the electrolytic reaction conditions:electrolyte solution of 1M H₂SO₄,solvent of H₂O,phase transfer catalyst of 0.01M sodium dodecyl benzene sulfonate,the concentration of toluene is200 ppm.Visible light and solar infrared energy are used simultaneously to drive the oxidation reaction of toluene to benzoic acid.The effect of solar thermal-electrical coupling effects in organic synthesis was studied.Through the regulation of the target product yield and selectivity,the optimal reaction conditions were obtained.Results indicate that elevated temperature and increased voltage contribute to the improvement of benzoic acid yielding.The yield reached the maximum value of 32%under the reaction temperature of 90?and the voltage of applied electric field of 3V.At this time,the selectivity of benzoic acid reaches the highest values,96.85%.The reaction mechanism at the surface of platinum electrode is free radical reaction for toluene oxidizing to benzoic acid by means of thermo-electric coupling model.?3?Considering the expensive platinum electrode,and the electro oxidation efficiency is not high under solar thermal-electric coupled fields.The effect of the functionalized graphite electrode on the synthesis of benzoic acid was studied by using of the graphite anode with reactive activity.Results indicate that the yield of benzoic acid achieved 8.8%at 30°C,11.4%at 60°C,and 37.7%at 90°C using an as-received graphite anode.The functionalized graphite anode produced even better yields;15.1%at 30°C,37.5%at 60°C and 44.6%at 90°C.These improvements are better than those for the expensive Pt anode alternative,at 12.4%at 60°C and 32.0%at 90°C,respectively.The analysis of the functionalized electrode showed an oxygenated surface and the presence of C-OH,C=O,and COOH groups at the graphite anode,which might help to adsorb the reactants,and the formation of the peroxides that can directly initiate the reaction to form benzoic acid.?4?We present the first demonstration of the three-field from solar energy?solar photo,solar electro,and solar thermo?,for high efficient organic synthesis of benzoic acid at the TiO₂ nanotubes electrode by adjusting the three-field,toluene is oxidized at the surface of the photoactive TiO₂ nanotubes electrode.Results showed that,the synergistic effect of the three-field of solar thermo,solar electro and solar photo,make the oxidation of toluene at TiO₂ electrode carried out easily.At the voltahe of 1.0V,the yield of benzoic acid and conversion of toluene improved greatly with temperature increase?30,60,90??,which reaches to 26.1%and 62.6%at 90?,respectively.The high temperature generated by solar thermal decreases the electrolysis potential of toluene oxidation,which is benefit for utilization of solar energy in STEP.There are many groups such as hydroxyl,carboxyl and-O-OH formed at the surface of TiO₂ nanotubes electrode,as well as the emergence of Ti-O-C bond at the surface of TiO₂,which leading to an increased visible absorption and significant enhancement of TiO₂ photocatalytic properties to increase the yield of benzoic acid.At meanwhile,the electric potential promotes the separation of photogenerated electrons and holes,and further prevents them from recombination so as to enhance the efficiency of TiO₂photocatalysis.A synergistic effect was found in the combination of solar photo,solar electro and solar thermo field for benzoic acid synthesis.