Faculty Publications

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Dye degradation studies using immobilized pristine and waste polystyrene-TiO2/rGO/g-C3N4 nanocomposite photocatalytic film in a novel airlift reactor under solar light
(Elsevier Ltd, 2019) Das, S.; Mahalingam, H.
Complex dyes are not completely removed in most wastewater treatment plants and thus released into nearby waterbodies posing problems to aquatic life and humans. In this study, a chemically synthesized nanocomposite photocatalyst containing TiO2, rGO and g-C3N4 immobilized in a polystyrene film is evaluated for the degradation of the Cu-phthalocyanine complex dye (Remazol Turquoise Blue, RTB) in a multiphase airlift reactor under sunlight. Both pristine and waste polystyrene were used in the synthesis of the film. The characterisation of the powder photocatalyst composite as well as the immobilized photocatalyst film is performed using particle size analyzer, SEM-EDX, BET, XRD, XPS, FTIR, and ICP-OES. The optimization of various parameters affecting the photocatalytic decolourization such as the g-C3N4 quantity in the composite catalyst, catalyst loading, the initial concentration of dye, use of waste polystyrene and catalyst reuse has been studied thoroughly. The photocatalytic treatment of RTB dye under optimum conditions for 90min shows that the decolourization (60%) and degradation (51.43%) as measured by TOC analysis are quite similar. The possible breakdown compounds from the parent molecule after the photocatalytic operation are identified by HPLC-MS. In conclusion, the immobilized nano-composite photocatalyst incorporated into a multiphase airlift reactor, is a very promising system to improve the water quality by TOC reduction, before discharge to nearby natural water sources. © 2019 Elsevier Ltd.
Novel immobilized ternary photocatalytic polymer film based airlift reactor for efficient degradation of complex phthalocyanine dye wastewater
(Elsevier B.V., 2020) Das, S.; Mahalingam, H.
Reduced graphene oxide (rGO) as well as graphitic carbon nitride (g-C3N4) catalysts were synthesized and a physical admixture of rGO and g-C3N4 along with TiO2 in the ratio of 1:1:1 by weight was immobilized in a polystyrene film using the facile solvent casting method. An internal loop airlift reactor with a working volume of 1.2 litres incorporating the prepared polymer-based photocatalytic film was designed and tested for the photocatalytic degradation of remazol turquoise blue dye synthetic wastewater. The reactor parameters affecting the photocatalytic activity such as airflow rate and Di/Do (ratio of draft tube diameter to outer tube diameter) were evaluated. The successful operation of the reactor obtained using the ternary immobilized catalyst mixture film gave 92.25% total organic carbon reduction and 94% decolourization within 140 min, compared to 91% decolourization by the slurry form within 40 min. Complete and quicker decolourization of the dye was also demonstrated under the influence of O3 or H2O2. The immobilized catalyst was successfully reused four times. The ternary catalyst admixture employed in this work and the unique design of the photocatalytic reactor helps to increase the degradation rate of toxic textile effluents thus making it suitable for larger scales of treatment. © 2019 Elsevier B.V.
Utilization of torrefied rice husk and deoiled cashew nut shell cake biomass waste for removal of hazardous Reactive Violet 5 dye
(Springer, 2025) Suriyakumar, S.; Mahalingam, H.; Sudhakar, R.D.
Torrefied biomass is a renewable, sustainable, carbon–neutral fuel that is replacing coal in many areas. This organic source has increased surface area and porosity, making it an effective adsorbent. Only a very few works have been reported in the literature on exploring the use of torrefied biomass and its ash as inexpensive adsorbents for the removal of dyes. In this work, rice husk and deoiled cashew nut shell cake in its torrefied and ash forms have been employed as adsorbents for Reactive Violet 5 dye removal. Thus, four adsorbents were synthesized and characterized by BET, SEM, XRD, and FTIR. The optimum parameters for maximum dye removal efficiency were 0.8 g/L adsorbent dosage, pH 2.0, and 40-min contact time for batch experiments using 100 mL of 10 ppm dye solution. The maximum adsorption capacity of torrefied rice husk, torrefied deoiled cashew nut shell cake, torrefied rice husk ash, and torrefied deoiled cashew nut shell cake ash were 108.58 mg/g, 88.38 mg/g, 68.0 mg/g, and 29.97 mg/g, respectively. Torrefied rice husk exhibited the best fit with the Freundlich isotherm, whereas other adsorbents fitted best with the Langmuir isotherm. The non-linear pseudo-second-order model gave the best fit. The intraparticle diffusion model showed that adsorption involves multiple diffusion stages. The thermodynamic parameters indicated that the process was spontaneous, feasible, and exothermic. These eco-friendly materials can be efficiently used in dye removal, thus paving the way for torrefied biomass or its ash to be used as low-cost adsorbents for large-scale wastewater treatment. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.

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