Green-engineered agricultural-based nano-adsorbent for efficient Cr(vi) removal: batch mechanisms and continuous...

Area of Science:

• Environmental Science
• Materials Science
• Green Chemistry

Background:

• Hexavalent chromium (Cr(vi)) poses significant risks to surface water ecosystems and human health.
• Conventional methods for Cr(vi) remediation are often costly and environmentally detrimental.
• Developing sustainable and efficient adsorbents is crucial for effective water treatment.

Purpose of the Study:

• To develop a green, cost-effective, and sustainable nano-adsorbent for Cr(vi) removal from surface water.
• To investigate the synergistic adsorption and photocatalytic properties of the developed material.
• To evaluate the material's performance in batch and continuous flow systems for practical application.

Main Methods:

• Synthesized a bio-based nano-adsorbent (A-WML/TiO2) from watermelon leaves and green-synthesized TiO2 nanoparticles using Cajanus cajan leaf extract.
• Characterized the adsorbent's surface area, functional groups, and adsorption-photocatalytic properties.
• Conducted batch adsorption experiments to optimize removal conditions (pH, dosage, concentration, time) and studied kinetics and isotherms.
• Performed fixed-bed column studies and regeneration tests to assess long-term performance and reusability.

Main Results:

• The acid-modified nano-adsorbent (A-WML/TiO2) achieved 94.23% Cr(vi) removal in batch experiments under optimal conditions (pH 4, 25 mg adsorbent, 10 ppm Cr(vi), 3 h).
• Photocatalytic activity reduced Cr(vi) to Cr(iii) with 81% efficiency under sunlight.
• Adsorption followed pseudo-second-order kinetics and Freundlich isotherm, indicating chemisorption and heterogeneous multilayer adsorption.
• The material demonstrated excellent stability over five regeneration cycles and significantly prolonged breakthrough time in fixed-bed columns.

Conclusions:

• The developed A-WML/TiO2 nano-adsorbent offers a highly efficient, sustainable, and dual-functional (adsorption-photocatalysis) solution for Cr(vi) remediation.
• The material's integration with sand filtration systems shows promise for scalable and practical continuous water treatment.
• This green approach presents a superior alternative to existing bio-adsorbents for hexavalent chromium removal.