Hydrothermal synthesis, characterization, and photocatalytic degradation of Rhodamine B dye of triazole modified molybdenum oxide

Abstract

Molybenuym oxide triazole [MoO₃(Htrz)_0.5]; Htrz = 1,2,4 Triazole] (Mo-Htz) was synthesized for the first time by hydrothermal route at 180 °C by using heteropolyacid as molybdenum source. The as-prepared material was characterized by X-Ray Diffraction (XRD), UV visible diffuse reflectance, thermal analysis, FT-IR and Raman spectroscopies. The XRD pattern shows narrow peaks and Mo-Htz crystallizes in an orthorhombic symmetry (SG: Pbcm): a/Å: 3.933(1), b/Å: 13.856(1), c/Å: 13.367(4). The crystal structure consists of Mo octahedron bonded to Htz molecules forming a layered structure with double [Mo₂O₆ (Htrz)]_n chains connected via a corner-sharing connection. Raman spectroscopy shows characteristic peaks of MoO, O–Mo–O and OMoO for MoO₃. The FT-IR spectrum corroborates the structure of the compound and confirms the existence of Htz and Mo–O bonds. SEM image displays a thin lamellar structure and EDS analysis quantify the elemental composition of a material.

The band gap energies change from 2.93 eV (bare MoO₃) to 2.95 eV (Mo-Htz) due to synergy effect. The current-potential (J-E) curve plotted in Na₂SO₄ electrolyte showed a medium hysteresis with electrochemical stability. The n-type semi conductivity, was indicated by negative slope of the capacitance⁻² - potential (C⁻² - E) graph and supported by the electrochemical impedance spectroscopy (EIS) under visible light illumination. The conduction band (4.19 eV/−0.56 V_SCE), is formed by the Mo⁶⁺: 3d orbital, where excited electrons reduce oxygen into O₂^•− radicals, involved in the Rhodamine B (Rh B) oxidation. An abatement of 60 % was reached by coupling “adsorption/photocatalysis” (5 h) under visible light. The degradation of Rh B follows a first order kinetic with a half-life of ∼3 h.