Rapid visible-light degradation of malachite green enabled by nanorod cobalt hydroxycarbonate: performance and mechanisms

Abstract

Morphological and crystal facet engineering to modulate band structure represents an effective strategy for enhancing the photocatalytic performance of semiconductor materials. Herein, a uniform nanorod-shaped cobalt hydroxycarbonate (COC-1) photocatalyst was synthesized via a one-step hydrothermal method using ethylene glycol as a structure-directing agent. Under visible light irradiation, the as-prepared COC-1 exhibited rapid and efficient degradation of malachite green (MG). Remarkably, with a catalyst loading of only 5 mg, COC-1 achieved 99.8% degradation of 50 mg·L⁻1 MG within 1 min, corresponding to a first-order rate constant of 6.2781 min⁻1 and a normalized rate constant (k′) of 0.1776 g·min⁻1·m⁻2. Well-defined nanorod morphology facilitates rapid charge transfer and effectively suppresses electron–hole recombination, thereby enhancing charge carrier dynamics and prolonging the excited-state lifetime, key factors contributing to its outstanding photocatalytic performance. Radical scavenging experiments and electron spin resonance (ESR) analysis identified superoxide radicals (•O2–), photogenerated holes (h+), and singlet oxygen (1O2) as the dominant reactive species governing the degradation process. Furthermore, the degradation pathway of MG was systematically elucidated by integrating experimental analyses with density functional theory (DFT) calculations and high-performance liquid chromatography–mass spectrometry (HPLC–MS). This work underscores the potential of COC-1 as a promising candidate for environmental wastewater remediation and offers valuable insights into the rational design of sustainable, high-performance photocatalysts.