In-situ synchronous carbonation and self-activation of biochar/geopolymer composite membrane: Enhanced catalyst for oxidative degradation of tetracycline in water

A new biochar/geopolymer composite membrane (BC/GM) was prepared by an in-situ synchronous carbonation and self-activation process from two sustainable materials. The monolithic geopolymer membrane (GM) served not only as a porous support, achieving good dispersion and retrieve of biochar (BC), but also as a solid base for in-situ activating BC during carbonization of lignin precursor. The obtained BC/GM contained a hierarchically porous structure (exhibiting a bi-modal pore size distribution at 3.54 and 16.53 nm, respectively), having a large specific surface area (37.46 m2/g, 28 times of BC), containing rich functional groups (COH, CO and OCO, etc.) and a high degree of graphitization (evidenced by a lower value of ID/IG = 0.81) which exhibited a high activity in decomposing H2O2 to generate ·OH radicals for degradation of tetracycline (TC). Nearly 100% of TC (50 mg/L, 100 mL) was removed by 0.15 g BC/GM (1 mL H2O2, pH 5.0, 60 °C, 5 h). It also showed a good stability and reusability during 5 repeated cycling. EPR, XPS, FTIR and Raman analysis suggested the phenolic-OH, ketone, quinone moieties and defect structures in BC contributed to the generation of ·OH through transferring electrons to H2O2, while the graphitized carbon in BC with porous structure and large surface area provided intimate contact between catalyst and TC molecules that accordingly enhanced the electron conductivity and suppressed the decay of ·OH radicals during redox reaction, which eventually realized the efficient degradation of TC into CO2, H2O, and other inorganic compounds through ring-opening reaction, isomerization, demethylation, deamination, and dehydration reaction.