A review on titanium oxide nanoparticles modified metal-organic frameworks for effective CO2 conversion and efficient wastewater remediation

Environmental pollution has been increasing since last decade due to increasing industrialisation and urbanisation. Various kinds ofenvironmental pollutants including carbon dioxide (CO2), dyes, pharmaceuticals, phenols, heavy metals along with many organic and inorganic species have been discovered in the various environmental compartments which possess harmful impacts tox human health, wildlife, and ecosystems. Thus, various efforts have been made through regulations, technological advancements, and public awareness campaigns to reduce the impact of the pollution. However, finding suitable alternatives to mitigate their impacts remained a challenge. Metal-organic frameworks (MOFs) are one of the advanced materials with unique features such as high porosity and stability which exhibit versatile applications in environmental remediation. Their composites with titanium oxide nanoparticles (TiO2) have been discovered to offer potential feature such as light harvesting capacity and catalytic activity. The composite integration and properties have been confirmed through characterization using surface area analysis, scanning electron/transmission electron microscopy, atomic force microscopy, fourier transformed infrared spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, and others. Thus, this work rigorously discussed potential applications of the MOF@TiO2 nanomaterials for the CO2 capture and effective utilization in methanol, ethanol, acetone, acetaldehyde, and other useful products that served as fuel to various industrial processes. Additionally, the work highlights the effective performance of the materials towards photocatalytic degradation of both organic and inorganic pollutants with indepth mechanistic insights. The article will offer significant contribution for the development of sustainable and efficient technologies for the environmental monitoring and pollution mitigation.

Application of a novel composite of Fe3O4@SiO2/PAEDTC surrounded by MIL-101(Fe) for photocatalytic degradation of penicillin G under visible light

The novel photocatalyst of Fe3O4@SiO2/PAEDTC@MIL-101(Fe) was prepared based on the sol-gel method, and its structure and morphology were determined by SEM mapping, TEM, XRD, FTIR, and N2 adsorption-desorption analyses. The photocatalytic activity of nanocomposite was evaluated in comparison with other particles as well as adsorption and photolysis processes. The effect of operating parameters showed that the complete degradation of penicillin G (PNG) can be provided at a photocatalyst dosage of 0.6 g/L, radiation intensity of 36 W, pH of 5, and time of 60 min. In the optimum condition, 84% TOC removal was attained and the BOD5/COD rate for the treated effluent was above 0.4, which was representative of the high biodegradability of the treated effluent compared to the raw sample. The findings of energy consumption showed that PNG can be easily and effectively treated by the photocatalytic process based on magnetic MIL-101(Fe) with electrical energy per order between 10 and 20.87 kWh/m3. Due to the excellent interaction between the MIL-101(Fe) and Fe3O4@SiO2/PAEDTC, the photocatalyst stability test showed a recyclability of the particles for 5 consecutive reaction cycles with a minimum reduction of 7%. Solution treated with photocatalyst under UV and visible light sources explained that the toxicity of the effluent after treatment is significantly reduced with the growth of Escherichia coli. Scavenging experiments showed that •OH radical and hole (h+) are the main agents in degrading PNG to CO2, H2O, and biodegradable and low-toxicity products. Finally, the findings of the diagnostic analysis and comparative experiments proved that with the interaction of Fe3O4@SiO2, NH2, and MIL-101(Fe), a lower band gap can be prepared for more absorption of photons and pollutant and also more and faster production of active radicals.

Construction of ternary (1D/2D/3D) Fe2O3-supported micro pillared Cu-based MOF on chitosan with improved photocatalytic behavior on removal of paraquat

A hetero-structured metal organic framework of Cu-BTC and Fe₂O₃ nano-photocatalyst were tethered over chitosan using the hydrothermal method and fabricated a hybrid porous nanocomposite (CS-Fe@Cu-BTC). X-ray diffractometer results exposed the existence of Fe₂O₃ peaks. Surface area measurements using BET showed a mesoporous structure and the formation of type IV adsorption isotherm for nanocomposite. XPS and SEM-EDAX confirmed the existence of Fe₂O₃ nanoparticles in the hybrid porous structure. The UV-vis diffuse reflectance absorption shape emphasized the role of Fe₂O₃ in enhancing the band gap of CS-Fe@Cu-BTC nanohybrid. The lower intensity photoluminescence spectra of the CS-Fe@Cu-BTC shows a competent charge partition and delayed the recombination of electron-hole pairs. The photo-mineralization efficiency of Cu-BTC and CS-Fe@Cu-BTC was evaluated in terms of electronic interactions using paraquat (PQT) as the probe molecule, which shows a mineralization of 91% at the pH range of ~ 5. The contribution of •OH in the degradation of PQT over CS-Fe@Cu-BTC nanocomposites revealed using the trapping test and the degradation mechanism follows the Langmuir-Hinshelwood model and pseudo-first-order kinetics. The durability of the CS-Fe@Cu-BTC nanocomposite was also established after four cycling processes.

Recent advances in application of metal-organic frameworks (MOFs) as adsorbent and catalyst in removal of persistent organic pollutants (POPs)

The presence of persistent organic pollutants (POPs) in the aquatic environment is causing widespread concern due to their bioaccumulation, toxicity, and possible environmental risk. These contaminants are produced daily in large quantities and released into water bodies. Traditional wastewater treatment plants are ineffective at degrading these pollutants. As a result, the development of long-term and effective POP removal techniques is critical. In water, adsorption removal and photocatalytic degradation of POPs have been identified as energy and cost-efficient solutions. Both technologies have received a lot of attention for their efforts to treat the world's wastewater. Photocatalytic removal of POPs is a promising, effective, and long-lasting method, while adsorption removal of persistent POPs represents a simple, practical method, particularly in decentralized systems and isolated areas. It is critical to develop new adsorbents/photocatalysts with the desired structure, tunable chemistry, and maximum adsorption sites for highly efficient removal of POPs. As a class of recently created multifunctional porous materials, Metal-organic frameworks (MOFs) offer tremendous prospects in adsorptive removal and photocatalytic degradation of POPs for water remediation. This review defines POPs and discusses current research on adsorptive and photocatalytic POP removal using emerging MOFs for each type of POPs.

Pesticide pollutants in the environment - A critical review on remediation techniques, mechanism and toxicological impact

The excessive and unorganised utilisation of pesticides have posed negative impacts on soil and water at higher levels. Pesticides are a major class of persistent organic compounds with high resistance to natural biodegradation and enhanced tendency to bio accumulate. The severe health hazards imposed on the living organisms hinder the ecosystem and lead to chronic and irreversible health issues. Photocatalytic method is reported as a potential alternative with a variety of techniques and materials that are safer, easier, durable, cost-effective and efficient. Nanomaterials play a key role in this domain due to their versatility. In particular, nanostructured materials of organized shapes and morphological properties have gained enormous attention in research and real-time applications. Specifically, nanomaterials like nanotubes, nanorods and nanowires have unique properties and anisotropic structure that make them more suitable for treating pesticide wastes with photocatalysis. Variety of tuning methods and materials are emerging to enhance the activity of titanium and zinc based nanocatalysts in remediation methods. In the present article, four pesticides, namely, atrazine, chlorpyrifos, paraquat and naphthalene are chosen due to their common occurrence and usage in agricultural applications. These pesticides are highly toxic and need special attention to explore appropriate remediation methods. The report also details the latest innovations reported by several research studies in exploring the potential of specially synthesised nanoparticles for photocatalytic removal of pesticide pollutants from environment. For zinc-based hybrid nanomaterials, the maximum disintegration reported were 99%, 98%, 73.3% and 92.3% for atrazine, chlorpyrifos, paraquat and naphthalene, respectively.

Synthesis, characterization, and application of α-Fe2 O3 @TiO2 @SO3 H photo-Fenton catalyst for photocatalytic degradation of biologically pre-treated wood industry wastewater

The efficiency of removing chemical oxygen demand (COD) and turbidity from wood wastewater was investigated using a sequencing batch reactor (SBR) and the photo-Fenton process. A total of 94.78% of COD reduction and 99.9% of turbidity removal were observed under optimum conditions of SBR, which consisted of an organic loading rate (OLR) of 0.453 kg COD m^-3  day^-1 , mixed liquor suspended solids (MLSS) of 4564 mg L^-1 , and cycle time of 48 h. A magnetic α-Fe₂ O₃ @TiO₂ @SO₃ H nanocatalyst was prepared as a heterogeneous Fenton reagent. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalyst. The response surface methodology (RSM) was used to optimize the process based on a central composite design (CCD). The maximum photocatalytic degradation of 87.54% and COD reduction of 83.35% were achieved at a dosage of 0.6 g L^-1 of catalyst, 30 mg L^-1 of H₂ O₂ , and pH of 3.5 for 45 min. The results indicated that a combination of the SBR process and α-Fe₂ O₃ @TiO₂ @SO₃ H could be used as an effective method for the treatment of wood wastewater. PRACTITIONER POINTS: A combination of the SBR and photo-Fenton process was introduced as an impressive method for wood industry wastewater treatment. The efficiencies of COD, BOD₅ , NO₃ -N, PO₄ -P, and color removal were obtained according to the standard limits in Iran. To our knowledge, this study is the first report of the use of synthesized α-Fe₂ O₃ @TiO₂ @SO₃ H photocatalyst for the wood industry wastewater treatment.

Hybrid metal organic frameworks as an Exotic material for the photocatalytic degradation of pollutants present in wastewater: A review

In this world, water is considered as the Elixir for all living creatures. Human life rolls with water, and every activity depends upon water. Worldwide water resources are being contaminated due to the elevation in the population count, industrialization and urbanization. Ejection of chemicals by industries and domestic sewages remains the major reason in the destruction of natural water resources. Contaminated water with harmful microbes, chemical dyes, pesticides, and carcinogens are the root cause of many diseases and deaths of living species. In this scenario, researchers engaged in producing ultra components to remove the contaminants. Metal organic frameworks (MOF) are the desired combination of organic and inorganic materials to achieve the required target. MOFs possess unique characteristics like tunable internal structure, porosity, crystallinity and high surface area which enable them for energy and environmental application. For the past years, MOFs are concentrated more as a photocatalyst in the treatment of polluted water. These research studies discuss the improvement of photocatalytic performance of MOF by the incorporation of metals, metal coupled with nanoparticles like polymers, graphene, etc., into it to achieve the enhanced photocatalytic activity by scavenging entire chemicals and harmful microbes to retain the quality of water. The target of this review article is to focus on the state of the art research work on MOFs in photocatalytic water treatment technique.

Preparation and application of α-Fe2O3@TiO2@SO3H for photocatalytic degradation and COD reduction of woodchips industry wastewater

In this study, we investigated the efficiency of photocatalytic degradation and chemical oxygen demand (COD) reduction from woodchips industry wastewater using α-Fe₂O₃@TiO₂@SO₃H. A magnetic α-Fe₂O₃@TiO₂@SO₃H was prepared as a heterogeneous photo-Fenton catalyst. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalysts. The response surface methodology (RSM) was used to optimize the photo-Fenton process based on a Box-Behnken design (BBD). The parameters such as catalyst dosage, H₂O₂ dosage, pH, and contact time on photocatalytic degradation and the reduction of COD were studied. The maximum photocatalytic degradation of 93.75% and COD reduction of 86.54% were achieved at a dosage of the catalyst of 1 g L^-1, H₂O₂ dosage of 40 mg L^-1, and a pH of 3.5 at 45 min. The kinetics of the photo-Fenton process was studied for the woodchips wastewater treatment under optimum conditions. The pseudo-second-order kinetic model for photocatalytic degradation and COD reduction was obtained. The results indicated that a α-Fe₂O₃@TiO₂@SO₃H could be used as an effective heterogeneous photocatalyst for the treatment of woodchips industry wastewater. Preparation and application of α-Fe₂O₃@TiO₂@SO₃H for photocatalytic degradation and COD reduction of woodchips industry wastewater.