Synthesis of 2D MoO3-x/N-doped-Carbon Nanocomposite via in situ Carbonization of Layered (NH4)Mo3O9-(NH4)2Mo4O13-Organic Hybrid Nanomaterials for Exceptionally Efficient Adsorption and Separation of Organic Dye

MoO3-x/N-doped-carbon (MoO3-x/N-C) nanocomposite with nanobelts structure was prepared by in situ carbonizations (NH4)Mo3O9-(NH4)2Mo4O13/oleylamine-oleic acid hybrids, which was designed using a two-step tailored nanoemulsion method followed by a solvothermal process. MoO3-x/N-C nanocomposite possesses high stability in a wide pH range of 1–11. In addition to the formation mechanism, detailed studies on adsorption properties, including adsorption isotherms, kinetics, mechanism, and reusability on MoO3-x/N-C nanocomposite, were systematically studied. The effect of various parameters for the adsorption characteristics, such as adsorbate concentration, contact time, pH, and temperature, were also evaluated. The detailed investigation of the kinetics and the adsorption mechanism of MB from an aqueous solution showed that the adsorption process follows a pseudo-second-order kinetic and intraparticle diffusion model. The adsorption isotherm study demonstrated that the Langmuir isotherm model could illustrate the experimental data with a maximum adsorption capacity value of ~1360 mg/g, which turns out to be the highest among the previously reported adsorbents based on MoO3 nanomaterials and attributed to multiple adsorption mechanisms including electrostatic, π–π stacking, and H-bonding interaction between MB dye and MoO3-x/N-C nanocomposite. Thermodynamic analysis suggested that MB adsorption onto MoO3-x/N-C nanocomposite was spontaneous and endothermic. Additionally, the adsorption and desorption cycle were examined for 100 ppm aqueous MB solution, where the removal efficiency by MoO3-x/N-C nanocomposite remained at ~99% even after four regeneration cycles. Furthermore, the MoO3-x/N-C nanocomposite could selectively adsorb MB from a binary solution mixture containing two times higher concentrations of an anionic dye, methyl orange (MO), and the separation efficiency obtained was ~99% at neutral pH. More significantly, the MoO3-x/N-C nanocomposite could successfully and simultaneously adsorb several cationic dyes, including MB, malachite green (MG), crystal violet (CV), safranin O (SO), and separate an anionic dye, MO, from quaternary and pentanary dye mixture solutions with a separation efficiency of ~75% and 62% respectively at neutral pH. The effective separation of a single component by oxide-based nanomaterials via a simple batch separation technique from a four/five-component mixed interfering analyte, close to a real matrix system, in an aqueous medium at neutral pH is not reported so far to the best of our knowledge. Therefore, MoO3-based nanocomposite could be a new promising material applied in dye wastewater treatment.

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