A simple strategy to design 3-layered Au-TiO2 dual nanoparticles immobilized cellulose membranes with enhanced photocatalytic activity

Highly stable Ag-doped Cu2O immobilized cellulose-derived carbon beads with enhanced visible-light photocatalytic degradation of levofloxacin

Ag-doped Cu2O immobilized carbon beads (Ag/Cu2O@CB) based composite photocatalysts have been prepared for the removal of levofloxacin, an antibiotic, from water. The photocatalysts were prepared by the processes of chemical reduction and in-situ solid-phase precipitation. The composite photocatalyst was characterized by a porous and interconnected network structure. Ag nanoparticles were deposited on Cu2O particles to develop a metal-based semiconductor to increase the catalytic efficiency of the system and the separation efficiency of the photogenerated carriers. Cellulose-derived carbon beads (CBs) can also be used as electron storage libraries which can capture electrons released from the conduction band of Cu2O. The results revealed that the maximum catalytic degradation efficiency of the composite photocatalyst for the antibiotic levofloxacin was 99.02 %. The Langmuir-Hinshelwood model was used to study the reaction kinetics, and the process of photodegradation followed first-order kinetics. The maximum apparent rate was recorded to be 0.0906 min-1. The mass spectrometry technique showed that levofloxacin degraded into carbon dioxide and water in the presence of the photocatalyst. The results revealed that the easy-to-produce photocatalyst was stable and efficient in levofloxacin removing.

Enhancing Photocatalytic Properties of TiO2 Photocatalyst and Heterojunctions: A Comprehensive Review of the Impact of Biphasic Systems in Aerogels and Xerogels Synthesis, Methods, and Mechanisms for Environmental Applications

This review provides a detailed exploration of titanium dioxide (TiO2) photocatalysts, emphasizing structural phases, heterophase junctions, and their impact on efficiency. Key points include diverse synthesis methods, with a focus on the sol-gel route and variants like low-temperature hydrothermal synthesis (LTHT). The review delves into the influence of acid-base donors on gelation, dissects crucial drying techniques for TiO2 aerogel or xerogel catalysts, and meticulously examines mechanisms underlying photocatalytic activity. It highlights the role of physicochemical properties in charge diffusion, carrier recombination, and the impact of scavengers in photo-oxidation/reduction. Additionally, TiO2 doping techniques and heterostructures and their potential for enhancing efficiency are briefly discussed, all within the context of environmental applications.

Structure and Photocatalytic Properties of Ni-, Co-, Cu-, and Fe-Doped TiO2 Aerogels

TiO₂ aerogels doped with Ni, Co, Cu, and Fe were prepared, and their structure and photocatalytic activity during the decomposition of a model pollutant, acid orange (AO7), were studied. After calcination at 500 °C and 900 °C, the structure and composition of the doped aerogels were evaluated and analyzed. XRD analysis revealed the presence of anatase/brookite and rutile phases in the aerogels along with other oxide phases from the dopants. SEM and TEM microscopy showed the nanostructure of the aerogels, and BET analysis showed their mesoporosity and high specific surface area of 130 to 160 m²·g^-1. SEM-EDS, STEM-EDS, XPS, EPR methods and FTIR analysis evaluated the presence of dopants and their chemical state. The concentration of doped metals in aerogels varied from 1 to 5 wt.%. The photocatalytic activity was evaluated using UV spectrophotometry and photodegradation of the AO7 pollutant. Ni-TiO₂ and Cu-TiO₂ aerogels calcined at 500 °C showed higher photoactivity coefficients (k_aap) than aerogels calcined at 900 °C, which were ten times less active due to the transformation of anatase and brookite to the rutile phase and the loss of textural properties of the aerogels.

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.

Natural Cotton Cellulose-Supported TiO2 Quantum Dots for the Highly Efficient Photocatalytic Degradation of Dyes

The artificial photocatalytic degradation of organic pollutants has emerged as a promising approach to purifying the water environment. The core issue of this ongoing research is to construct efficient but easily recyclable photocatalysts without quadratic harm. Here, we report an eco-friendly photocatalyst with in situ generated TiO₂ quantum dots (TQDs) on natural cotton cellulose (CC) by a simple one-step hydrothermal method. The porous fine structure and abundant hydroxyl groups control the shape growth and improve the stability of nanoparticles, making natural CC suitable for TQDs. The TQDs/CC photocatalyst was synthesized without the chemical modification of the TQDs. FE-SEM and TEM results showed that 5-6 nm TQDs are uniformly decorated on the CC surface. The long-term stability in photocatalytic activity and structure of more than ten cycles directly demonstrates the stability of CC on TQDs. With larger CC sizes, TQDs are easier to recycle. The TQDs/CC photocatalysts show impressive potential in the photocatalytic degradation of anionic methyl orange (MO) dyes and cationic rhodamine B (RhB) dyes.

Photocatalytic nanohybrid membranes for highly efficient wastewater treatment: A comprehensive review

Wastewater is inevitably generated from human activities as part of the life cycle chain that potentially damages the environment. The integration of photocatalytic reaction and membrane separation for wastewater treatment has gained great attention in recent studies. However, there are still many technical limitations for its application such as toxic metal release, catalyst deactivation, fouling/biofouling, polymer disintegration, and separation performance decline. Different types, combinations, and modifications of photocatalysts material combined with membranes such as semiconductor metal oxides, binary/ternary hybrid metal oxides, elemental doped semiconductors, and metal-organic frameworks (MOFs) for improving the performance and compatibility are presented and discussed. The strategies of incorporating photocatalysts into membrane matrix for pursuing the most stable membrane integrity, high photocatalytic efficiency, and excellent perm-selectivity performance in the very recent studies were discussed. This review also outlines the performance enhancement of photocatalytic membranes (PMs) in wastewater treatment and its potential for water reclamation. Photocatalysts enhanced membrane separation by inducing anti-fouling and self-cleaning properties as well as antibacterial activity. Based on the reviewed study, PMs are possible to achieve complete removal of emerging contaminants and ∼99% reduction of bacterial colony that leading on the zero liquid discharge (ZLD). However, the intensive exposure of photo-induced radicals potentially damages the polymeric membrane. Therefore, future studies should be focused on fabricating chemically stable host-membrane material. Moreover, the light source and the membrane module design for the practical application by considering the hydrodynamic and cost-efficiency should be a concern for technology diffusion to the industrial-scale application.

Photocatalytic membranes: a new perspective for persistent organic pollutants removal

The presence of conventional and emerging pollutants infiltrating into our water bodies is a course of concern as they have seriously threatened water security. Established techniques such as photocatalysis and membrane technology have proven to be promising in removing various persistent organic pollutants (POP) from wastewaters. The emergence of hybrid photocatalytic membrane which incorporates both photocatalysis and membrane technology has shown greater potential in treating POP laden wastewater based on their synergistic effects. This article provides an in-depth review on the roles of both photocatalysis and membrane technology in hybrid photocatalytic membranes for the treatment of POP containing wastewaters. A concise introduction on POP's in terms of examples, their origins and their effect on a multitude of organisms are critically reviewed. The fundamentals of photocatalytic mechanism, current directions in photocatalyst design and their employment to treat POP's are also discussed. Finally, the challenges and future direction in this field are presented.

Role of Oil Palm Empty Fruit Bunch-Derived Cellulose in Improving the Sonocatalytic Activity of Silver-Doped Titanium Dioxide

In this study, a novel cellulose/Ag/TiO₂ nanocomposite was successfully synthesized via the hydrothermal method. The cellulose extracted from oil palm empty fruit bunch (OPEFB) could address the disposal issue created by OPEFB biomass. Characterization studies such as FESEM, EDX, HRTEM, XRD, FTIR, UV-Vis DRS, PL, XPS, and surface analysis were conducted. It was observed that the incorporation of cellulose could hinder the agglomeration, reduce the band gap energy to 3 eV, increase the specific surface area to 150.22 m³/g, and lower the recombination rate of the generated electron-hole pairs compared to Ag/TiO₂ nanoparticles. The excellent properties enhance the sonocatalytic degradation efficiency of 10 mg/L Congo red (up to 81.3% after 10 min ultrasonic irradiation) in the presence of 0.5 g/L cellulose/Ag/TiO₂ at 24 kHz and 280 W. The improvement of catalytic activity was due to the surface plasmon resonance effect of Ag and numerous hydroxyl groups on cellulose that capture the holes, which delay the recombination rate of the charge carriers in TiO₂. This study demonstrated an alternative approach in the development of an efficient sonocatalyst for the sonocatalytic degradation of Congo red.

Porous Silica Microspheres with Immobilized Titania Nanoparticles for In-Flow Solar-Driven Purification of Wastewater

In this paper, inorganic silica microspheres with interconnected macroporosity are tested as a platform for designing robust and efficient photocatalytic systems for a continuous flow reactor, enabling a low cost and straightforward purification of wastewater through solar-driven photocatalysis. The photocatalytically active microspheres are prepared by wet impregnation of porous silica scaffolds with Trizma-functionalized anatase titania (TiO2) nanoparticles (NPs). NPs loading of 22 wt% is obtained in the form of a thin and well-attached layer, covering the external surface of the microspheres as well as the internal surface of the pores. The TiO2 loading leads to an increase of the specific surface area by 26%, without impacting the typically interconnected macroporosity (≈60%) of the microspheres, which is essential for an efficient flow of the pollutant solution during the photocatalytic tests. These are carried out in a liquid medium for the decomposition of methyl orange and paracetamol. In addition to photocatalytic activity under continuous flow, the microspheres offer the advantage that they can be easily removed from the reaction medium, which is an appealing aspect for industrial applications. In this work, the typical issues of TiO2 NPs photocatalysts are circumvented, without the need for elaborate chemistries, and for low availability and expensive raw materials.

All-cellulose functional membranes for water treatment: Adsorption of metal ions and catalytic decolorization of dyes

In this study, we present a facile, one-step method for the manufacturing of all-cellulose, layered membranes containing cellulose nanocrystals (CNC), TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical)-mediated oxidized cellulose nanofibers (TO-CNF), or zwitterionic polymer grafted cellulose nanocrystals (CNC-g-PCysMA) as functional entities in combination with cellulose fibers and commercial grade microfibrillated cellulose. The presence of active sites such as hydroxyl, carbonyl, thioethers, and amines, gave the membranes high adsorption capacities for the metal ions Au (III), Co (II), and Fe (III), as well as the cationic organic dye methylene blue (MB). Furthermore, the membranes served as excellent metal-free catalysts for the decolorization of dyes via hydrogenation. A 3-fold increase of the hydrogenation efficiency for cationic dyes such as rhodamine B (RhB) and methylene blue was obtained in the presence of membranes compared to NaBH₄ alone. Water-based processing, the abundance of the component materials, and the multifunctional characteristics of the membranes ensure their potential as excellent candidates for water purification systems.

Impact of Titanium Dioxide (TiO2) Modification on Its Application to Pollution Treatment—A Review

A high-efficiency method to deal with pollutants must be found because environmental problems are becoming more serious. Photocatalytic oxidation technology as the environmentally-friendly treatment method can completely oxidate organic pollutants into pollution-free small-molecule inorganic substances without causing secondary pollution. As a widely used photocatalyst, titanium dioxide (TiO2) can greatly improve the degradation efficiency of pollutants, but several problems are noted in its practical application. TiO2 modified by different materials has received extensive attention in the field of photocatalysis because of its excellent physical and chemical properties compared with pure TiO2. In this review, we discuss the use of different materials for TiO2 modification, highlighting recent developments in the synthesis and application of TiO2 composites using different materials. Materials discussed in the article can be divided into nonmetallic and metallic. Mechanisms of how to improve catalytic performance of TiO2 after modification are discussed, and the future development of modified TiO2 is prospected.