Abstract
The development of visible-light-driven polymeric g-C3N4 is in response to an emerging demand for the photocatalytic dye degradation and reduction of hexavalent chromium ions. We report the synthesis of g-C3N4 from urea treated with various solvents such as methanol, ethanol, and ethylene glycol. The samples were characterized and the Williamson–Hall method was applied to investigate the lattice strain of the samples. The activity of the samples was evaluated by observing the degradation of methyl orange and K2Cr2O7 solution under light irradiation. Photocatalytic reaction kinetics were determined as pseudo-first-order and zero-order for the degradation of methyl orange and reduction of hexavalent chromium, respectively. Due to the inhibited charge separation resulting from the small lattice strain, reduced crystal imperfection, and sheet-like structure, g-C3N4 obtained from ethanol-treated urea exhibited the highest activity among the evaluated samples.
Highlights
Aqueous dye solutions of methyl blue, methyl orange, rhodamine B, Congo red, etc., are commonly adopted in the textile, paper, leather, pharmaceutical, and cosmetic industries, and often cause serious problems when discharged into water resources [1,2,3]
The present results suggest that urea-derived g-C3 N4 exhibits high photocatalytic activity for the degradation of methyl orange (MO) and reduction of Cr(VI) ions, and that pretreatment of the precursor using ethanol is an effective technique for reducing the defect density and improving the photocatalytic activity of g-C3 N4
The W–H method simultaneously considers the lattice strain and the crystallite size of the sample based on Equation (1), otherwise termed the uniform deformation model (UDM): βhklcosθ = (Kλ/DW-H ) + 4εsinθ where βhkl is the peak width at half-maximum intensity of the plane, DW–H accounts for the crystallite size, K is a constant, λ is the wavelength of the incident X-ray (1.5418 Å for CuKα radiation), and ε represents the lattice strain from crystal imperfection and distortion
Summary
Aqueous dye solutions of methyl blue, methyl orange, rhodamine B, Congo red, etc., are commonly adopted in the textile, paper, leather, pharmaceutical, and cosmetic industries, and often cause serious problems when discharged into water resources [1,2,3]. The removal of Cr(VI) and degradation of dye molecules in the effluent of the textile industry through photocatalytic processes to achieve a sustainable, green, and cost-effective approach is an urgent demand. Photocatalytic materials could activate under UV and/or visible light to generate active species, such as photoexcited electrons, holes, hydroxyl radicals, and superoxide radicals, to trigger the degradation [7,8,9] of dyes and reduction of metal ions (e.g., Cr(VI) , As(V) ) [10,11]. Researchers worldwide have focused on g-C3 N4 because of its high thermal and chemical stability, visible light activity, unique electronic properties, and ease of synthesis. The high thermal and chemical stability of g-C3 N4 is Polymers 2019, 11, 182; doi:10.3390/polym11010182 www.mdpi.com/journal/polymers
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