Mesoporous Ca-alginate/melamine-rich covalent organic polymer/cupric oxide-based microgel beads as heterogeneous catalyst for efficient catalytic reduction of hazardous water pollutants

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Present work focused on employing the advantages of novel porous melamine-rich covalent organic polymer (MCOP)-nano cupric oxide (CuO)–based heterogeneous catalysts for catalytic reduction of diverse pollutants including aromatic nitro compounds (p-nitrophenol, o-nitrophenol), toxic dyes (rhodamine B, methylene blue, congo red, methyl orange), and heavy metal ions (chromium(VI)). First, nano-CuO was prepared in a green process, and MCOP was fabricated by a solvothermal method. Subsequently, MCOP@CuO hybrids were developed. To improve the recyclability and stability of the MCOP@CuO hybrids and prevent secondary contamination by the powdery form of hybrids in the water, microgel beads based on alginate substrate were developed. First, the fabricated catalysts were employed for p-nitrophenol reduction, and the effect of catalyst loading and NaBH4 concentration were optimized. In optimum conditions, the catalytic reduction of other pollutants was tested and kinetic studies were examined. Furthermore, the proposed mechanisms for catalytic reductions were presented. Ca-alginate/MCOP@CuO microgel beads efficiently and successfully reduced toxic contaminants in a short time. All pollutants were removed in the time range of 14–55 min. Conversion percentages in removing pollutants were obtained at 90–98% for Ca-alginate/MCOP@CuO Ex-situ microgel beads. These microgel beads were greatly stable and effortlessly recycled without loss of their performance (for 5 consecutive cycles). The kinetics data were fit to the pseudo-first-order model with good correlation coefficients (R2 > 98). Such microgel-based catalysts will expose an innovative frontier in design materials for different potential requests such as treating toxic pollutants.