Kojic-Acid-Driven Innovation: Developing Biocompatible and Versatile Catalysts for Sustainable CO₂ Conversion

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.