Study On The Preparation Of Bio-based Iron-carbon Material And Its Application On Hydrogen Production By Dark Fermentation

With the rapid development of industrialization,energy crisis and environmental deteriorations turn into the primary obstacles of social development.Hydrogen（H₂）is a clean energy which can replace traditional fossil fuels.Bio-H₂ production by dark fermentation has received much more attention because of its wide source of raw materials,low cost and energy consumption,simple equipment and operation.The solid organic wastes were used as raw materials to prepare bio-based carbon materials and synthetise new functional carbon meterals with trace elements（such as iron and manganese）.The new materials have unique phy-chemical properties and can be used as additive to improve the performance of H₂ producing bacteria for dark fermentation.To achieve the goal of combining organic waste treatment and clean energy production,the main work of this paper can be summarized as follows:（1）Biochar（BC）was prepared by corn-bran residue（CBR）with a specific surface area of 58.232 m²/g and used as an additive in the H₂ evolution by dark fermentation.The physicochemical characteristics of BC and its effects were investigated in this paper.It was found that the higher concentration of BC,the higher cumulative H₂ production（CHP）in the appropriate range.The maximum CHP of 204mL/g-glucose was harvested with 600 mg/L of BC and was 29.11%higher than that of the control group.However,the CHP decreased when BC concentration increased to800 mg/L.In addition,the effects of Fe²⁺on dark fermentation were analyzed.It was found that the H₂ yields increased gradually when the Fe²⁺concentration ranged from 0to 200 mg/L.And the maximum H₂ yield was 217.4 mL/g-glucose,which was 37%higher than that of the control group.Nevertheless,the CHP decreased when Fe²⁺concentration increased to 300 mg/L.Besides,the synergistic effects of BC and Fe²⁺on hydrogen production were studied.It was showed that the largest H₂ yield was harvested at the ratio of 3:1 of BC/Fe²⁺(600 mg/L BC and 200 mg/L Fe²⁺),which（234.4 mL/g-glucose）increased by 50%compared with the control group.In anaerobic fermentation system,BC can enrich microorganisms,provide sufficient gathering places for the growth and metabolism of microorganisms,promote the formation of biofilm,and enhance the resistance of hydrogen-producing bacteria to the external environment.Fe is an essential element for the growth and metabolism of microorganisms which has important roles on the synthesis of intracellular ferric reductant protein and hydrogenase.（2）Fe₂O₃/biochar nanomaterials（FOCNPs）were synthesized by starch and Fe²⁺.The FOCNPs with a specific surface area of 27.63 m²/g were composed of Fe₂O₃ and BC.The applications and effects of FOCNPs on H₂ production were investigated.It was found that the maximum CHP was obtained at the FOCNPs concentration of 200mg/L,and the H₂ yield（218 mL/g-glucose）increased by 33.7%compared with the control group.The maximum potential hydrogen production rate estimated by the kinetic model was 32.41 mL/g·h^-1,which was 8.6%higher than that of the control group.However,when the concentration of FOCNPs exceeded 200 mg/L,hydrogen production was inhibited.Fe²⁺consisted in FOCNPs was release to the system slowly by the action of microbial metabolites,providing essential factors for microbial growth and enzyme synthesis;FOCNPs have huge specific surface area which can enrich microorganisms;In addition,nano-FOCNPs can be used as semiconductor materials to provide electron transfer channels for microorganisms and accelerate the electron transfer rate between microorganisms.（3）Magnetic Fe₃O₄/activated carbon materials（MAC）were synthesized by activated carbon（AC）and Fe²⁺.The main components of the material were AC,Fe₃O₄and a small amount of Fe₂O₃.And the specific surface area of MAC was 45.78 m²/g.It was found that the composition of MAC could provide adequate conditions to improving the growth and metabolism of microorganisms.When the concentration of MAC was 200 mg/L,the maximum H₂ yield was 214 mL/g-glucose,which was 64.8%higher than that of the control group.The H₂ yield decreased when the dosage of MAC exceeded 200 mg/L.At the same time,the MAC can be separated by magnetic because of the consist of Fe₃O₄ and realize the recovery and utilization of activated carbon.（4）Manganese doped magnetic carbon materials（MDMC）were synthesized by AC,Fe²⁺and Mn²⁺,and its main components were activated carbon,MnFe₂O₄ and a small amount of Fe₃O₄ and MnCO₃.The specific surface area of MDMC was 110.92m²/g.The MDMC were applied to anaerobic fermentation under mesophilic（37°C）and thermophilic（55°C）conditions,respectively.It was found that the maximum hydrogen production was 211 mL/g-glucose when the concentration of MDMC was400 mg/L at 37°C,which was 55.8%higher than that of the control group.Fe²⁺and Mn²⁺loaded in the material can provide essential elements for the growth and metabolism of hydrogen-producing bacteria.MAC can enrich microorganisms and improve their hydrogen production performance.Meanwhile,the materials have magnetism and can be easily separated from the system after fermentation,which is conducive to the recovery and utilization of carbon materials.The study found that bio-based iron-carbon materials were synthesized by carbon materials which obtained from the carbonization of organic solid waste and essential trace elements（iron and manganese）have different functions.The application of the carbon materials in the process of hydrogen production by dark fermentation could improve the activity and concentration of hydrogen-producing microorganisms,thus promoting their hydrogen production performance.