Bias-free photoelectrochemical degradation of organic pollutant with a TiO2-based photoanode decorated with Mg(OH)2 nanodiscs

We present a photoelectrode based on TiO2 nanoparticles wrapped in electrochemically reduced graphene oxide (ERGO) and decorated with Mg(OH)2 nanodisc (ND) for the efficient photoelectrochemical (PEC) degradation of methylene blue (MB) as a model compound under sunlight without the need for external voltage. The photoelectrode was fabricated through a simple two-step electrochemical process involving the co-deposition of TiO2 nanoparticles on ERGO, followed by reductive electrochemical decoration with Mg(OH)2ND. Structural, morphological, and photoelectrochemical characterizations revealed that the electrochemically synthesized hierarchical heterostructure promoted charge separation through hole-blocking Mg(OH)2 nanodiscs and enhanced light absorption via Ti3+ defects and oxygen vacancies. The Mg(OH)2ND-ERGO/TiO2 photoelectrode showed a significant enhancement in PEC degradation performance compared to the bare ERGO/TiO2. Under optimized conditions, the modified photoelectrode achieved 94.6 % MB degradation within 150 min, representing a 15-fold increase in efficiency compared to ERGO/TiO2. Scavenger experiments revealed that superoxide radicals (center dot O2-) played a predominant role in the degradation mechanism. The photoelectrode demonstrated excellent batch-tobatch consistency and long-term stability over multiple degradation cycles. This work demonstrates that the potential of the Mg(OH)2ND-ERGO/TiO2 nanocomposite functions as an efficient and stable photoelectrode for solar-driven PEC degradation of organic pollutants without the need for external power, offering a promising energy-efficient solution for environmental remediation.