Enhancement of H2-water mass transfer using methyl-modified hollow mesoporous silica nanoparticles for efficient microbial CO2 reduction

Abstract

Inorganic-microbial hybrid catalysis is an emerging technology that uses electrical energy to drive microorganisms to reduce CO₂ into high value-added compounds, and it has broad application prospects in CO₂ reduction. However, the low current density (production yield) limits its practical application. Hydrogen-mediated inorganic-microbial hybrid catalysis system can achieve higher current density, but it is limited by low H₂ mass transfer. Here, silica nanoparticles were used to enhance the hydrogen mass transfer for highly efficient CO₂ reduction. Solid silica (SN), mesoporous silica (MSN), hollow mesoporous silica (HMSN), and methyl-modified hollow mesoporous silica (MHMSN) were firstly prepared and tested for the enhancement of hydrogen mass transfer. Of these, MHMSN nanoparticles at a concentration of 0.3 wt% were the best at enhancing gas-liquid mass transfer, the volumetric mass transfer coefficient (K_La) and saturated dissolved hydrogen concentration of H₂ are 0.53 min^-1 and 1.81 mg l^-1, respectively. Compared with the control group without added nanoparticles, MHMSN significantly increased the solubility and K_La of H₂. This can be attributed that the addition of MHMSN promoted the detached process of hydrogen bubbles from the electrode surface, which made the diameter of hydrogen bubbles smaller, increased the gas-liquid mass transfer area, and strengthened the mass transfer process of H₂. Furthermore, it was added to the inorganic-microbial hybrid catalysis system to effectively promote the microbial carbon reduction process, achieving a polyhydroxybutyrate (PHB) yield of up to 700 mg l^-1, and the electron utilization rate and CO₂ conversion rate were 51 % and 58 % higher than the control group, respectively. These results demonstrated that the addition of MHMSN is an effective approach to enhancing the performance of H₂-mediated inorganic-microbial hybrid catalysis system.