The escalating global challenge of wastewater contamination by persistent organic pollutants necessitates the development of sustainable, cost-effective, and highly efficient visible-light-driven photocatalysts. Motivated by this challenge, this study presents the sustainable transformation of bio-waste precursors, such as rice husk and egg shells, into Ca2SiO4 (RE) composites and their functionalization with ZnO nanoparticles (REZ) and Zn0.95Cu0.05O nanoparticles (RECZ) for visible-light-driven photocatalysis. XRD analysis suggests the formation of polycrystalline composites, comprising major calcium silicate phases, primarily Ca2SiO4 and Ca3SiO5. The FESEM–EDS analysis showed that Zn0.95Cu0.05O addition in the RE nanocomposite results in a denser, more uniform microstructure compared to the porous, agglomerated structure of RE. UV-visible-DRS results exhibit a reduction in the effective optical band-gap energy from 2.20 eV (RE) to 2.05 eV (RECZ), indicating enhanced visible-light absorption. PL emission results reveal a decrease in emission intensity from RE to RECZ, suggesting suppressed radiative recombination and improved charge separation due to defect-related trapping states. Among all samples, the RECZ nanocomposite exhibits the highest visible-light photocatalytic degradation of the MB dye, achieving a maximum efficiency of 90.4% in 180 min at an optimal catalyst load of 30 mg. Furthermore, the scavenger and OH radical tests indicated that superoxide (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:{{\bullet\:}O}_{2}^{-}\)</EquationSource> </InlineEquation>) and hydroxyl radicals (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\:{\bullet\:}\text{O}\text{H}\)</EquationSource> </InlineEquation>) are the dominant reactive species involved in the degradation of MB. Additionally, the RECZ nanocomposite exhibits stability and reusability, with strong photocatalytic activity over five consecutive cycles. These results highlight the synergistic effectiveness of waste-derived Ca2SiO4 composite functionalized with Zn0.95Cu0.05O nanoparticles in producing efficient, durable, and sustainable photocatalysts for wastewater treatment. This work indicates a sustainable waste-to-photocatalyst strategy utilizing rice husk and eggshell-derived calcium silicate as an effective support for Cu-doped ZnO under visible-light irradiation.

Enhanced visible-light photocatalytic activity of Cu-doped ZnO functionalized waste-derived calcium silicate-based composites

期刊论文
发表日期：

2026年5月29日

查看全文

Madhu A,
Areej S Alqarni,
Satyanarayana Reddy S,
K Santhosh,
Rudresh Kumar K J,
Srinatha N

摘要

The escalating global challenge of wastewater contamination by persistent organic pollutants necessitates the development of sustainable, cost-effective, and highly efficient visible-light-driven photocatalysts. Motivated by this challenge, this study presents the sustainable transformation of bio-waste precursors, such as rice husk and egg shells, into Ca₂SiO₄ (RE) composites and their functionalization with ZnO nanoparticles (REZ) and Zn_0.95Cu_0.05O nanoparticles (RECZ) for visible-light-driven photocatalysis. XRD analysis suggests the formation of polycrystalline composites, comprising major calcium silicate phases, primarily Ca₂SiO₄ and Ca₃SiO₅. The FESEM–EDS analysis showed that Zn_0.95Cu_0.05O addition in the RE nanocomposite results in a denser, more uniform microstructure compared to the porous, agglomerated structure of RE. UV-visible-DRS results exhibit a reduction in the effective optical band-gap energy from 2.20 eV (RE) to 2.05 eV (RECZ), indicating enhanced visible-light absorption. PL emission results reveal a decrease in emission intensity from RE to RECZ, suggesting suppressed radiative recombination and improved charge separation due to defect-related trapping states. Among all samples, the RECZ nanocomposite exhibits the highest visible-light photocatalytic degradation of the MB dye, achieving a maximum efficiency of 90.4% in 180 min at an optimal catalyst load of 30 mg. Furthermore, the scavenger and OH radical tests indicated that superoxide ( \(\:{{\bullet\:}O}_{2}^{-}\) ) and hydroxyl radicals ( \(\:{\bullet\:}\text{O}\text{H}\) ) are the dominant reactive species involved in the degradation of MB. Additionally, the RECZ nanocomposite exhibits stability and reusability, with strong photocatalytic activity over five consecutive cycles. These results highlight the synergistic effectiveness of waste-derived Ca₂SiO₄ composite functionalized with Zn_0.95Cu_0.05O nanoparticles in producing efficient, durable, and sustainable photocatalysts for wastewater treatment. This work indicates a sustainable waste-to-photocatalyst strategy utilizing rice husk and eggshell-derived calcium silicate as an effective support for Cu-doped ZnO under visible-light irradiation.