Biochar-Modified TiO2 Composites: Enhanced Optical and Photocatalytic Properties for Sustainable Energy and Environmental Applications

Enhancing TiO2 performance is essential for advancing photocatalysis, environmental remediation, and energy conversion technologies. In this work, nanosized TiO2 was modified with biochar (BC) derived from red sea algae at different loadings (0, 5, 10, and 15 wt%). Structural analysis confirmed that TiO2 maintained its crystalline framework while biochar introduced additional amorphous features and modified surface morphology. Optical measurements revealed a redshift in the absorption edge and tunable bandgap values (3.28–3.72 eV), accompanied by increases in refractive index and extinction coefficient, indicating enhanced light–matter interactions. Electrochemical studies demonstrated that the TiO2/5 wt% BC composite exhibited the lowest charge-transfer resistance and highest peak current, reflecting superior conductivity. Photocatalytic tests showed that TiO2/5 wt% BC achieved nearly 84% degradation of methylene blue within 150 min under visible-light irradiation, with stable reusability over multiple cycles. These findings demonstrate that moderate biochar incorporation (5 wt%) optimally enhances the physicochemical, electrochemical, and photocatalytic properties of TiO2, making it a promising candidate for wastewater treatment, solar-driven catalysis, and sustainable energy applications.