Mechanism And Thermodynamic Analysis Of Biological Hydrogen Production Promoted By Nanomaterials Based On (AQS) Synthesis Of Anthraquinone-2-sulfonate Sodium

As a kind of renewable clean energy,hydrogen?H₂?has attracted the attention of researchers all over the world when the energy problem is becoming more and more serious.At present,there are many methods to prepare hydrogen,among which the main methods are:hydrogen production by water hydrolysis,hydrogen production from natural gas and hydrogen production from biomass.Compared with other hydrogen production methods,hydrogen production from biomass has the advantages of wide range of raw materials,low cost,no secondary pollution and so on.However,at present,the output of biological hydrogen production is difficult to meet the industrial demand,because the essence of biological hydrogen production is to consume the electrons accumulated in the biological body through H⁺,and the hydrogen production efficiency of biological dark fermentation is low.therefore,it is worth studying to improve the efficiency of biological hydrogen production by microorganisms.In this paper,the mechanism and thermodynamic analysis of hydrogen production by biological dark fermentation promoted by nanoparticles were deeply studied.Most researchers have reported the biological hydrogen production from glucose and the thermodynamics of the hydrogen production process,but the thermodynamics of biological hydrogen production from xylose has not been reported yet.Therefore,the thermodynamics of Klesiella oxytoca GS-4-08 formic acid cracking pathway in the conversion of pentose to biological hydrogen production was studied in this paper.Represented by xylose,an important hemicellulose hydrolysis product,the complete stoichiometric reaction equation of xylose fermented by Klebsiella was constructed on the basis of electronic equivalent balance,and then the Gibbs free energy of each reaction was calculated.The results of thermodynamic analysis showed that the step of fermenting xylose to acetyl-CoA was the thermodynamic bottleneck of all batch experiments.Considering that the actual pulp and papermaking wastewater usually contains lignocellulose wastes and dyeing agents and other pollutants,this paper investigated the hydrogen production of xylose in the presence of dyes.Taking the xylose solution containing azo dyes as the representative,Klebsiella was analyzed by means of thermodynamics to decolorize azo dyes while producing hydrogen from xylose.The results showed that compared with the system without azo dye?2.14 mol H₂/mol sugar?,the molar yield of hydrogen with 0.3 mM methyl red?MR?dye decreased by 0.12 mol H₂/mol sugar?2.02 mol H₂/mol sugar?.Thermodynamic analysis showed that there was a significant change in the??G^o?'value of formic acid cracking hydrogen production and ethanol production.This may be due to the fact that the presence of MR affects the activities of formate hydrolyase?FHL?and ethanolase.In this paper,it is proved that the presence of 0.1 mM MR can inhibit the activities of formate hydrolyase?FHL?and ethanolase,so it can be concluded that formic acid cleavage and ethanol production are thermodynamic bottlenecks in the presence of carboxyl azo dye MR,and the change of Gibbs free energy may be caused by the inhibition of enzyme activity.According to the previous research of our group,anthraquinone-2-sulfonate?AQS?can be used as a redox mediator?RM?to promote extracellular electron transfer.In this study,it is reported for the first time that AQS@rGO nanoparticles may be used as RM to accelerate the biological reduction of azo dyes.The adsorption capacity of the prepared AQS@rGO to anionic azo dyes is weak,but in the presence of GO,the biological reduction rate of AQS@rGO nanoparticles to MO is increased by 1.5-2 times in both batch experiment and sequencing batch reactor?AnSRB?.At the same time,the EPR signal of solid AQS@rGO quinone radical was also measured in this study.The experimental results show that the prepared AQS@rGO has a stable and efficient catalytic effect on the biological decolorization of MO during the 7-cycle AnSRB operation cycle.The acceleration of the reduction of azo dyes by AQS@rGO may be due to the formation of the space charge layer,which promotes the effective charge transfer from the highly conductive rGO films to the Czochralski group of AQS molecules.As an efficient and economical RM,compared with the reported soluble and insoluble RM,the prepared AQS@rGO has the characteristics of high efficiency,low cost and reusability.Because the essence of the process of biological hydrogen production is to release hydrogen through the combination of protons and electrons,thus consuming the electrons accumulated in the biological fermentation process.In previous studies,it has been found that free anthraquinone-2-sulfonate?AQS?can be used as a redox mediator?RM?to promote extracellular electron transfer,and it has been found that free AQS can be immobilized on reduced graphene oxide?rGO?to prepare AQS@rGO nanoparticles.In this paper,it is reported for the first time that AQS@rGO nanoparticles may be used as RM to accelerate the biological reduction of azo dyes.The adsorption capacity of the prepared AQS@rGO to anionic azo dyes is weak,but in the presence of graphene oxide?GO?,the biological reduction rate of AQS@rGO nanoparticles to methyl orange?MO?is increased by 1.5-2 times in both batch experiments and sequencing batch reactor?AnSRB?.At the same time,the electron paramagnetic resonance?EPR?signal of solid AQS@rGO quinone radical was also measured in this study.The experimental results show that the prepared AQS@rGO has a stable and efficient catalytic effect on the biological decolorization of MO during the 7-cycle AnSRB operation cycle.The acceleration of the reduction of azo dyes by AQS@rGO may be due to the formation of the space charge layer,which promotes the effective charge transfer from the highly conductive rGO films to the Czochralski group of AQS molecules.Compared with the reported ratio of soluble and insoluble RM,the prepared AQS@rGO nanoparticles are a highly efficient and economical RM with high efficiency,low cost,and reusability.The above results show that the AQS@rGO nanomaterials synthesized in this study can be used as RM to promote the extracellular electron transfer in the process of biodegradation of MO,but the extracellular electron transfer in the process of biological hydrogen production promoted by AQS@rGO nanomaterials as RM remains to be explored.Therefore,this paper used Klesiella oxytoca GS-4-08 as a model strain to explore the effect of AQS@rGO nanoparticles on hydrogen production by dark fermentation of xylose in Klesiella oxytoca GS-4-08.Firstly,the effect of temperature on hydrogen production by dark fermentation of xylose in Klesiella oxytoca GS-4-08was investigated.The results showed that 35^oC was the best reaction temperature for hydrogen production by dark fermentation of xylose in Klesiella oxytoca GS-4-08.At this temperature,the activity of hydrogenase in organism was the highest,and the cumulative hydrogen production could reach 0.154196 mol H₂/mol sugar.When the temperature was higher than 35^oC,the hydrogen production decreased off the cliff,but when the temperature was lower than 35^oC,the hydrogen production decreased slowly.This has a improtant significance for the application of dark fermentation biological hydrogen production in large-scale production.