Authors: Santosh Kumar
Source: RMIT (article, 2026-01-01)
Field: Chemistry — Analytical Chemistry

Synthesis of Surface-Modified Photocatalysts for Efficient Degradation of Polychlorinated Biphenyls and Dyes The degradation of water quality due to anthropogenic pollution continues to challenge environmental sustainability and public health on a global scale. Industrial discharges, agricultural runoff, and domestic effluents have led to the contamination of freshwater systems with toxic substances, including polychlorinated biphenyls (PCBs) and synthetic dyes. These pollutants persist in aquatic environments, disrupt ecological balance, and pose serious health risks when they enter drinking water supplies or accumulate in the food chain, demanding the development of integrated strategies for both their detection and remediation. A critical requirement in addressing such contaminants lies in their trace-level detection and accurate quantification, especially in complex environmental matrices such as surface water. In the present work, the first step was dedicated to developing a robust and sensitive analytical method for monitoring LC-PCBs. Seven different congeners representing mono-, di-, and tri-chlorinated classes were selected to evaluate extraction performance across varied structural configurations comprehensively. A solvent-based microextraction approach was designed and systematically optimised using Central Composite Design (CCD), allowing fine-tuning of extraction parameters to maximise recovery of targeted analytes. The optimised method was subsequently evaluated for its analytical robustness through parameters such as sensitivity, linearity, and reproducibility. The optimised LLME method achieved excellent analytical performance, with linearity greater than R2 = 0.998 across 7.8–1000 µg L-1, limits of detection (LOD) ranging from 0.04–1.3 µg L-1, and recoveries between 73.3–106.7%. Precision values (RSD &lt; 8%) confirmed reproducibility. These assessments confirmed the method’s capability to detect and quantify selected PCBs congeners at environmentally relevant concentrations, with consistent performance across repeated measurements. Its reliability and operational stability made it well-suited for practical application in field-collected samples. Accordingly, the method was employed for the extraction of LC-PCBs from surface water samples obtained from sites along the Ganga River in Kanpur and Prayagraj. To interpret the spatial distribution and potential sources of contamination, the extracted data were further analysed using multivariate statistical tools, offering insight into the pattern and extent of LC-PCBs pollution across the studied regions. Building upon this foundation, the second phase of the study focused on the green synthesis of multifunctional nanomaterials for use in contaminant degradation. A collection of composite photocatalysts has been created, featuring Zinc oxide (ZnO) and Titanium dioxide (TiO2) nanoparticles, along with TiO2-doped ZnO (Zno@TiO2) nanocomposites. Surface modifications were further applied using polyethylenimine (PEI) to TiO2-doped ZnO (ZnO@TiO2/PEI) nanocomposites to improve interfacial charge transfer and pollutant interaction. The materials were synthesised via eco-friendly protocols utilising plant extracts and characterised using standard analytical techniques to confirm morphology, structural features, and optical properties. The Citrus limetta–assisted synthesis produced uniformly dispersed nanocomposites (nanometric crystallite size), with enhanced BET surface area (66.6 m2 g-1) and a positive zeta potential (+5.2 mV; point zero charge ≈ 10–11), confirming improved dispersion and interfacial charge transfer capability. The rationale behind the design was to integrate photocatalytic efficiency with surface-functional characteristics suitable for organic pollutant degradation. In the third phase, the application of these nanocomposites was explored for the photocatalytic degradation of 2,3-dichlorobiphenyl, also known as PCB-5, selected as a representative of LC-PCBs. Photodegradation experiments were conducted under natural sunlight to simulate environmentally realistic conditions. To understand the active degradation pathway, quenching studies and mechanistic investigations were employed, focusing on the identification of reactive species involved in the transformation process. Under optimised solar conditions, the ZnO@TiO2/PEI nanocomposite achieved &gt;95 % degradation of PCB-5 in 60 min (99 % at ~75 min), outperforming the individual oxides and the unmodified heterojunction; mechanistic quenching indicated hydroxyl radicals (•OH) and superoxide radicals (O2•⁻ or SORs) participation. This section aimed to evaluate the photocatalytic capability of the synthesised nanocomposites in degrading chlorinated pollutants under sustainable operating conditions. In the fourth phase, the photocatalytic potential of the synthesised nanocomposites was further investigated for the degradation of a ternary mixture of industrial dyes, comprising Reactive Orange 16, Congo Red, and BBG. These dyes were selected as representatives of commonly encountered synthetic colourants in textile effluents. The degradation experiments were conducted under solar irradiation to reflect ambient operational conditions. To enhance degradation efficiency, key degradation process parameters were systematically optimised using CCD, while environmental indicators such as pH, dissolved oxygen, and total organic carbon were concurrently monitored to evaluate water quality throughout the reaction course. The optimised system achieved &gt; 91 % total colour removal within 90 min under solar irradiation; response-surface models showed a strong quadratic model fit, confirming robust predictive reliability across the tested design space. This part of the study aimed to assess the versatility and effectiveness of nanocomposites in remediating complex mixtures of organic pollutants beyond PCB treatment. Overall, the study presents a coherent framework that integrates analytical development, green nanomaterial synthesis, photocatalytic optimisation, and environmental application under realistic conditions. Limitations related to catalyst reuse, large-scale deployment, and long-term field stability are acknowledged, and future work is recommended to improve pilot-scale validation and real-effluent remediation for sustainable water treatment. Pollutant ; Contamination ; Robustness (evolution) ; Water quality ; Effluent ; Pollution ; Water pollution ; Extraction (chemistry) Analytical chemistry methods development ; Toxic Organic Pollutants Impact ; Pharmaceutical and Antibiotic Environmental Impacts