Unveiling surface chemistry effects of Zn2GeO4 nanorods on their photocatalytic activity on dyes and photo-oxidation of ethylene glycol

Abstract

This study combines experimental and theoretical approaches to investigate the photocatalytic activity and ethylene glycol (EG) photo-oxidation capabilities of Zn2GeO4 (ZGO) nanorods. The semiconductor was synthesized via the hydrothermal method at 140°C for 120 min using varying water:EG ratios (v/v). Powder X-ray diffraction and Rietveld refinement confirmed a single-phase rhombohedral phenacite structure for the samples ZGO-0 (100:0, water:EG), ZGO-25 (75:25), ZGO-50 (50:50), and ZGO-75 (25:75), while ZGO-100 (0:100) exhibited a mixed-phase composition. Increasing EG content reduced crystallite and particle sizes, resulting in larger surface areas and negative zeta potentials. FTIR and Raman analyses indicated the presence of residual EG on the ZGO surfaces, influencing photocatalytic activity. Among the single-phase samples, ZGO-0 achieved the highest dye degradation efficiency (>99 % methylene blue and >64 % rhodamine B after 120 min), while ZGO-75 showed the lowest activity when normalized by surface area (k/SBET). Time-resolved photoluminescence spectroscopy and kinetic modeling demonstrated that EG photo-oxidation follows pseudo-second-order and parabolic diffusion mechanisms, suggesting physisorption-driven adsorption and diffusion-limited electron transfer. Density functional theory (DFT) calculations confirmed that EG adsorption is energetically favorable on the (001) and (2−21) facets, in agreement with experimental results. These findings establish ZGO as a promising photocatalyst and potential biofuel catalyst, highlighting the role of facet-specific interactions and surface chemistry in tuning catalytic performance.