Metal‐Free Semiconductor‐Based Bio‐Nano Hybrids for Sustainable CO₂‐to‐CH₄Conversion with High Quantum Yield

Abstract

Bio‐nano hybrids with methanogens and nano‐semiconductors provide an innovative strategy for solar‐driven CO2‐to‐CH4 conversion; however, the efficiency mismatch between electron production and utilisation results in low quantum yield and CH4 selectivity. Herein, we report the integration of metal‐free polymeric carbon nitrides (CNx) decorated with cyanamide (NCN) groups and Methanosarcina barkeri (M. b). The self‐assembled M. b‐NCNCNx exhibited a quantum yield of 50.3 % with 92.3 % CH4 selectivity under illumination, which outperforms other reported bio‐nano hybrid systems and photocatalytic systems for CO2 reduction. This excellent performance was attributed to the distinct capacitance and conductive effects of NCNCNx, which promoted electron storage and redistribution at the biotic–abiotic interface to alleviate recombination losses and side reaction. This study provides new design guidelines for bio‐nano hybrids for the sustainable photocatalytic reduction of CO2 into fuels.

Sustainable Conversion of Microplastics to Methane with Ultrahigh Selectivity by a Biotic–Abiotic Hybrid Photocatalytic System

“…The PLA‐to‐CH 4 performance with M. b ‐CDPCN was further evaluated with a light–dark cycle of 12 h to mimic the day–night cycles (Figure 3C). CH 4 yields not only increased under illumination but continued to increase in the dark, which could be partly attributed to the accumulated reductive species and intermediates (e.g., NADH, NADPH, ferredoxin, and acetyl‐CoA) under illumination that could be used in the dark cycle [10, 21] . Importantly, an increased CH 4 production rate was observed during the light–dark cycles (Figure 3C), because the high concentration of small organic intermediates via the photooxidation pathway, such as pyruvate and acetate, acted as the effective carbon and energy sources for M. b (demonstrated in the following part).…”

“…In contrast, the living biocatalysts have the highly specific biological catalytic power and self‐reproducing capacity, which can solve the limitation of photocatalysis [9] . For this reason, a great attention has been paid to biotic‐abiotic hybrid (biohybrid) systems that can take advantage of both photocatalysis and biocatalysis [10] . As demonstrated in recent years, the integration of light‐harvesting semiconductors with whole‐cell biocatalysts via intimate connections in a biohybrid system, along with sacrificial quenchers as continuous electron donors, can drive the specific solar‐to‐biofuel conversion [11] .…”

“…[9] For this reason, a great attention has been paid to biotic-abiotic hybrid (biohybrid) systems that can take advantage of both photocatalysis and biocatalysis. [10] As demonstrated in recent years, the integration of light-harvesting semiconductors with whole-cell biocatalysts via intimate connections in a biohybrid system, along with sacrificial quenchers as continuous electron donors, can drive the specific solar-to-biofuel conversion. [11] Although the biohybrid systems have not been demonstrated for treating plastic wastes, we here propose that plastic wastes such as microplastics may serve as a promising alternative to the expensive and unsustainable chemical sacrificial quenchers for the biohybrid systems.…”

“…CH 4 is chosen as a target product due to its high calorific value of 890 kJ mol À 1 and can be integrated into the existing energy infrastructure. [10] As a proof of concept, the self-assembled M. b-CDPCN resulted in a sustainable high-grade CH 4 production (> 99.5 %), along with the 90.2 % mineralization of poly(lactic acid) (PLA) that was pretreated at 180 °C for 1 h. Further research validated the real-world applicability of the M. b-CDPCN hybrid system by converting non-biodegradable microplastics such as polystyrene (PS), polyethylene terephthalate (PET), and polyurethane (PUR) films into CH 4 . This study offers a unique and sustainable approach toward the efficient conversion of plastic wastes into valuable fuels with high mineralization efficiency and product selectivity.…”

Solar-driven methanogenesis with ultrahigh selectivity by turning down H2 production at biotic-abiotic interface

“…The limitations become more prominent when methane (CH 4 ), which has a high calorific value of 890 kJ mol −1 and can be integrated into the existing energy infrastructure, is chosen as the target product 6 . The conversion of CO 2 to CH 4 is a kinetically complex and energetically intensive process that involves multiple protoncoupled electron transfer steps and requires to finely tune activation energy for promoting the forward reaction 7 . Solar-driven CO 2 -to-CH 4 conversion is an ideal approach in terms of energy input, and yet is largely limited by unsatisfactory reaction activity and product selectivity.…”