Ultrasound-assisted synthesis of biomass-derived carbon-supported binary metal oxides for efficient adsorption of heavy metals from wastewater

Abstract

Heavy metal contamination in water sources remains a critical environmental issue, primarily due to industrial activities, in terms of its continuous contribution to pollution through non-compliance and illegal discharge. This study presents an innovative biochar-supported binary metal oxide composite (nickel oxide (NiO) and cobalt oxide (CoO) nanoparticles) synthesized via ultrasound-assisted techniques for efficient adsorption of Zn(ii) and Cd(ii) ions from wastewater. By utilizing solid residues and leveraging ultrasound technology, this approach aligns with the principles of green chemistry due to utilization of a renewable biomass-based source, enhancing energy efficiency in the synthesis process, and minimizing waste production. Thereby a sustainable and innovative route for material development is explicitly demonstrated. Structural and morphological characterizations confirm the uniform integration of Nickel oxide (NiO) and cobalt oxide (CoO) particles into the biochar matrix, leading to maximum adsorption capacities of 18.9 mg g^-1 for Zn(ii) and 10.2 mg g^-1 for Cd(ii). The adsorption process follows a chemisorptive monolayer mechanism, as demonstrated by kinetic and isotherm studies, and is thermodynamically confirmed to be endothermic and spontaneous. The material also exhibits excellent reusability over five adsorption-desorption cycles. By integrating sustainable resources with innovative synthesis techniques, this work contributes to advancing wastewater remediation technologies while supporting global sustainability initiatives.

Fig. 1. XRD patterns of blank bio-char, and CoO/NiO@bio-char materials.

Fig. 2. FTIR spectra of both pure bio-char and CoO/NiO@bio-char.

Fig. 3. Raman spectroscopy charts for both blank bio-char and CoO/NiO@bio-char.

Fig. 4. SEM and EDX spectra of CoO/NiO@biochar.

Fig. 5. Isotherms and PSD curves of blank bio-char (I and II) and CoO/NiO@bio-char (III and IV).

Fig. 6. Particle size distribution of blank bio-char (I), and CoO/NiO@bio-char (II).

Fig. 7. Sorption efficiency of Zn(ii), and Cd(ii) depending on (I) function of solution pH (mixing time: 240 min; room temperature; initial concentration: 40 mg L⁻¹; and sorbent dose: 3.0 g L⁻¹), and (II) sorbent dose (room temperature; initial concentration of 40 mg L⁻¹; shaking time of 240 min; solution pH 5.9).

Fig. 8. (I) The kinetic curve of Zn(ii) and (II) Cd(ii) uptake process (solution pH 5.9; temperature of 25 ± 1 °C; initial concentration of 40 mg L⁻¹; sorbent dosage of 3.0 g L⁻¹).

Fig. 9. (I) Isotherm profile for the adsorption of Zn(ii) and (II) Cd(ii) ions from aqueous using CoO/NiO@bio-char (temperature of 25 ± 1 °C; pH 5.9; sorbent dosage of 3.0 g L⁻¹; shaking time is 240 min).

Fig. 10. (I) impact of reaction temperature of Zn(ii) and Cd(ii) sorption capacity (40 mg L⁻¹ initial concentration; sorbent dose of 3.0 g L⁻¹; pH 5.9; shaking time is 120 min), (II) thermodynamic profile for the adsorption process.

Fig. 11. FTIR (I), Raman (II), and EDX spectra (III) for spent adsorbent.

Fig. 12. The proposed sorption mechanisms for Zn(ii), and Cd(ii) ions on CoO/NiO@bio-char sorbent.

Fig. 13. Zn(ii), and Cd(ii) desorption from loaded CoO/NiO@bio-char sorbent using different solutions (3.0 g L⁻¹, room temperature; 240 min).