Fabrication and characterization of inverse opal tin dioxide as a novel and high-performance photocatalyst for degradation of Rhodamine B dye

Biopolymer‑carbonaceous composites, progress, and adsorptive mitigation of water pollutants

Chitin is the second most abundant natural biopolymer, which is composed of N-acetyl glucosamine units linked by β-(1 → 4) Chitosan is an N-deacetylated product of chitin. Properties of chitosan and chitin, such as biocompatibility, non-toxic nature, and biodegradability, make them successful alternatives for energy and environmental applications. However, their low mechanical properties, small surface area, reduced thermal properties, and greater pore volume restrict the potential for adsorption applications. Multiple investigations have demonstrated that these flaws can be prevented by fabricating chitosan and chitin with carbon-based composites. This review presents a comprehensive analysis of the fabrication of chitosan/chitin carbon-based materials. Furthermore, this review examines the prevalent technologies of functionalizing chitosan/chitin biopolymers and applications of chitin and chitosan as well as chitosan/chitin carbon-based composites, in various environmental fields (mitigating diverse water contaminants and developing biosensors). Also, the subsequent regeneration and reuse of adsorbents were also discussed. Finally, we summarize a concise overview of the difficulties and potential opportunities associated with the utilization of chitosan/chitin carbon-based composites as adsorbents to remove water contaminants.

Cellulose/inorganic nanoparticles-based nano-biocomposite for abatement of water and wastewater pollutants

Nanostructured materials offer a significant role in wastewater treatment with diminished capital and operational expense, low dose, and pollutant selectivity. Specifically, the nanocomposites of cellulose with inorganic nanoparticles (NPs) have drawn a prodigious interest because of the extraordinary cellulose properties, high specific surface area, and pollutant selectivity of NPs. Integrating inorganic NPs with cellulose biopolymers for wastewater treatment is a promising advantage for inorganic NPs, such as colloidal stability, agglomeration prevention, and easy isolation of magnetic material after use. This article presents a comprehensive overview of water treatment approaches following wastewater remediation by green and environmentally friendly cellulose/inorganic nanoparticles-based bio-nanocomposites. The functionalization of cellulose, functionalization mechanism, and engineered hybrid materials were thoroughly discussed. Moreover, we also highlighted the purification of wastewater through the composites of cellulose/inorganic nanoparticles via adsorption, photocatalytic and antibacterial approach.

Engineered inverse opal structured semiconductors for solar light-driven environmental catalysis

Inverse opal (IO) macroporous semiconductor materials with unique physicochemical advantages have been widely used in solar-related environmental areas. In this minireview, we first summarize the synthetic methods of IO materials, emphasizing the two-step and three-step approaches, with the typical physicochemical properties being compared where applicable. We subsequently discuss the application of IO semiconductors (e.g., TiO₂, ZnO, g-C₃N₄) in various photo-related environmental techniques, including photo- and photoelectro-catalytic organic pollutant degradation in water, optical sensors for environmental monitoring, and water disinfection. The engineering strategies of these hierarchical structures for optimizing the activities for different catalytic reactions are discussed, ranging from heterojunction construction, cocatalyst loading, and heteroatom doping, to surface defect construction. Structure-activity relationships are established correspondingly. With a systematic understanding of the unique properties and catalytic activities, this review is expected to orient the design and structure optimization of IO semiconductor materials for photo-related performance improvement in various environmental techniques. Finally, the challenges of emerging IO structured semiconductors and future development directions are proposed.

Core-shell magnetic molecularly imprinted polymer for selective recognition and detection of sunset yellow in aqueous environment and real samples

Magnetic Molecularly imprinted polymers (MMIPs) have been recently recognized as an exceptional tool for monitoring and decontamination of environmental and biological samples of diverse nature. Based on the potential applications as sorbents and biomimetic sensors, herein, a core-shell magnetic-molecularly imprinted polymer (MMIP) was developed as a selective material for separation and sensing of sunset yellow (SY) dye in an aqueous environment and real samples. The MMIP was synthesized via precipitation polymerization using SY as a template, MAA as a functional monomer (chosen based on simulation studies), EGDMA as a cross-linking agent, and AIBN as an initiator. To elaborate the specificity of MMIP, a comparative agent, magnetic non-imprinted polymer (MNIP) was also synthesized. The XRD results showed that the MMIP showed both crystalline and amorphous structure attributed to the presence and polymeric and non-polymeric groups. The FTIR spectra confirmed synthesis of intermediate and final MMIP product. The SEM results showed spherical morphology and porous structure of the MMIP with an average particle size of 0.636 μm in diameter. The MMIP was first employed as a sorbent for the removal of SY from the aqueous environment. The binding experiments performed at optimized operating conditions (pH 2; time 30 min; sorbent dosage 3 mg; sorbate concentration 80 ppm) showed more selectivity when compared with MNIP. The data fitted best to Langmuir's sorption isotherm (Q_o 359.8 mg/g) and followed the pseudo-second-order kinetic model. The synthesized MMIP was also used as an electrochemical sensor for detection of SY dye in the aqueous environment, which exhibited a linear range of detection as (1.51 × 10^-6 - 1.5 × 10^-3 M). The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.00413 M and 0.0137 M, respectively. While the R² value was found to be 0.997 at optimized analytical conditions. These results suggested that the synthesized MMIP can be applied for the selective separation and quantification of SY dye in sample of diverse nature.

High Efficient and Cost Effective Titanium Doped Tin Dioxide Based Photocatalysts Synthesized via Co-precipitation Approach

High efficient and large surface area of titanium doped tin dioxide (SnO2) based photocatalysts with various titanium doping contents varying from 0 to 4 mol% have been successfully prepared via a facile, low cost and eco-friendly co-precipitation method. Structural, morphological, textural, microstructural and optical properties of the prepared Ti-SnO2 nanoparticles (NPs) have been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), the Brunauer–Emmett-Teller (BET) method, Raman spectroscopy, Fourier transform infrared (FTIR), UV-Vis spectroscopy and photoluminescence (PL) spectroscopy. It was found that both undoped and Ti doped SnO2 NPs were crystallized in tetragonal structure and the crystallite sizes have been reduced from 19.9 nm for undoped SnO2 NPs to 13.1 nm for SnO2: Ti 4%. As compared to pure SnO2, a decrease in size and a uniform distribution of spherical aggregates for 4% Ti doped SnO2 sample have been noticed. Nitrogen (N2) adsorption-desorption isotherms of all synthesized NPs indicate that each nanopowder showed a IV type- isotherm with a hysteresis loop resulted in a typical porous materials containing macropores and mesopores. The raman spectra was marked with the appearance of three well resolved peaks including one intense peak centered at 633 cm−1 and two other peaks at about 475 cm−1 and 772 cm−1 which might be ascribed to the characteristic modes of of the SnO2 rutile-type. FTIR spectra of Ti doped SnO2 NPs show a broad band situated in the region from 630 cm−1 to 625 cm−1 for all Ti–SnO2 samples which could be assigned to the stretching vibrations of Sn–O–Sn. Optical studies revealed that the absorption edge of SnO2: Ti NPs showed a redshift with rising titanium concentration. This redshift resulted in a decrease in the optical band gap from 3.31 eV for pure SnO2 to 2.87 eV for 4% Ti doped SnO2 nanoparticles respectively. Rhodamine B dye (RhB) has been adopted to study the photocatalytic degradation of all synthesized Ti–SnO2 NPs. Pure SnO2 NPs has an intrinsic large band gap and it was sensitive to UV light. Thus, pure SnO2 NPs display higher UV photocatalytic performance for decomposing the RhB. Titanium incorporation into SnO2 has widely improved its photocatalytic performance towards RhB photodegradation under UV and Visible light irradiations. Precisely, the 4% Ti–SnO2 based photocatalyst display the highest photacatalytic activity and can degrade both of 95% and 52% of RhB dye within 120 min respectively under UV and visible light irradiations. The enhanced photocatalytic activity of the 4% doped SnO2 photocatalyst was further proved with the minimum PL intensity. The homogeneous incorporation of low Ti contents into the SnO2 matrix allow to a significant reduce in the band gap leading to an efficient separation of photogenerated electron-hole pairs and consequently improves the absorption capability in the visible light.