Introduction
This study develops eco-friendly catalysts using kojic acid, halloysite nanotubes, and alginic acid to create sustainable materials for CO2 reduction and fixation.
Methods
HNTs functionalized with KA (HNT-KAs) wwere synthesized by reacting HNTs with chloroKA (ClKA) in DMF at 80 °C overnight, using Et3N as a base. The use of three ClKA ratios produced HNT-KA1, HNT-KA3, and HNT-KA6. FT-IR confirmed their functionalization, and TGA was used to assess their thermal stability. SEM-EDX and TEM characterized their morphological properties. CO2 photoconversion experiments were conducted under simulated solar irradiation for 7 hours, using hydrogen as the reducing agent in the presence of copper ions. Copper, chelated by the KA moiety, was introduced via CuCl2 and reduced into Cu(I) using ascorbic acid. AA functionalized with KA (AA-KA) was synthesized through nucleophilic substitution with ClKA in dry DMF at 40 °C. Both catalysts were tested for their CO2 fixation into cyclic carbonates at 70 °C and 1 atm using TBAB as a co-catalyst. Styrene epoxide was used as the model substrate, and the catalysts' recyclability was evaluated based on their insolubility in organic solvents.
Results
HNT-KA6 showed the best performance among the tested ratios, achieving 31% CO2 photoreduction into methane and 89% CO2 conversion into cyclic carbonates, surpassing the same values for HNT-KA1 and HNT-KA3. Adding Cu(I) increased the CO2 photoreduction efficiency threefold and the methane selectivity fourfold while maintaining the stability over four cycles. HNT-KA6 also demonstrated strong CO2 fixation activity without copper, as KA facilitated CO2 capture and opening of the epoxide ring. AA-KA was highly efficient, achieving optimal yields with a continuous CO2 flow at 70 °C for 10 hours. Both catalysts worked effectively under mild, solvent-free conditions, delivering higher yields than those previously reported.
Conclusions
The HNT-KA6 and AA-KA catalysts demonstrate high potential for sustainable CO2 conversion. Their efficiency under mild, solvent-free conditions and their excellent recyclability make them ideal for green chemistry, supporting eco-friendly solutions for climate change mitigation.
