La–ZnO/silica aerogel derived from rice husk for adsorption and photocatalytic removal of petroleum contaminants from produced water

Produced water generated from oil and gas operations represents one of the largest and most complex industrial wastewater streams, characterized by persistent petroleum hydrocarbons that are difficult to remove using conventional separation or adsorption-based technologies. Existing treatment approaches often suffer from limited efficiency, poor regenerability, or an inability to simultaneously capture and mineralize dissolved hydrocarbons. In this context, multifunctional materials that integrate adsorption and photocatalytic degradation within a single platform have emerged as promising alternatives. La–ZnO/silica aerogel composite was synthesized using rice husk-derived silica and evaluated for the removal of petroleum hydrocarbons from aqueous systems. Structural analyses (XRD, FTIR, SEM, and BET) confirmed the uniform dispersion of La–ZnO nanoparticles within the aerogel matrix, producing a hierarchical meso–macroporous network with enhanced surface area and stability. Adsorption studies revealed pseudo-second-order kinetics and a strong fit with the Langmuir model, indicating chemisorption on homogeneous sites with a maximum monolayer capacity of ∼150 mg g −1 . Under simulated solar irradiation (AM 1.5G), the composite exhibited superior photocatalytic activity compared with bare La–ZnO, achieving rapid degradation with an apparent rate constant ( k app ≈ 0.014 min −1 ). total organic carbon and chemical oxygen demand reduction confirmed significant mineralization (>50% within 240 min), while recyclability tests demonstrated high structural stability and sustained performance over multiple cycles. Mechanistic evaluation highlighted a synergistic “adsorb-and-degrade” pathway, supported by La-induced bandgap modification and aerogel-assisted pollutant pre-concentration. These findings demonstrate the potential of La–ZnO/silica aerogels as sustainable, high-performance materials for treating complex petroleum-contaminated waters.