Enhanced photocatalytic decomposition of phenol in wastewater by using La-TiO2 nanocomposite

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Phenolic compounds induce ferroptosis-like death by promoting hydroxyl radical generation in the Fenton reaction

Phenolic compounds are industrially versatile chemicals, also the most ubiquitous pollutants. Recently, biosynthesis and biodegradation of phenols has attracted increasing attention, while phenols' toxicity is a major issue. Here, we evolved phloroglucinol-tolerant Escherichia coli strains via adaptive evolution, and three mutations (ΔsodB, ΔclpX and fetAB overexpression) prove of great assistance in the tolerance improvement. We discover that phloroglucinol complexes with iron and promotes the generation of hydroxyl radicals in Fenton reaction, which leads to reducing power depletion, lipid peroxidation, and ferroptosis-like cell death of E. coli. Besides phloroglucinol, various phenols can trigger ferroptosis-like death in diverse organisms, from bacteria to mammalian cells. Furthermore, repressing this ferroptosis-like death improves phloroglucinol production and phenol degradation by corresponding strains respectively, showing great application potential in microbial degradation or production of desired phenolic compounds, and phloroglucinol-induced ferroptosis suppresses tumor growth in mice, indicating phloroglucinol as a promising drug for cancer treatment.

Removal of ethylene by synthesized Ag/TiO2 photocatalyst under visible light irradiation

Photocatalysts based on titanium dioxide (TiO₂) were widely applied to solve environmental problems such as water and air pollution treatment. Currently, the application of these compounds for food packaging is increasing. This study prepared silver (Ag) doped TiO₂ photocatalyst (Ag/TiO₂) for the decomposition of gas ethylene (Eth), which is the main factor that causes fruits to over-ripen and damage or decay. It found that the doping of Ag could improve the optical property and light adsorption ability of Ag/TiO₂ photocatalyst, which directly enhanced the photocatalytic decomposition of Eth performance. Under visible light, Ag/TiO₂ could depredate 91.2% of Eth, while the removal performance by using the original TiO₂ was 43.9%. The increased initial concentration of Eth from 5 to 30 ppm could inhibit the photocatalytic efficiency of Ag/TiO₂ from 98.6 to 69.2%. Besides, the relative humidity and gas flow rate are roles in the Eth decomposition process. The recycling experiment confirmed that Ag/TiO₂ had good reusability with a slight loss in photocatalytic performance (18.6%) after ten cycles tested. The future protective application of Ag/TiO₂ for food protection during storage and transportation is discussed. This work provides a potential method to remove gas ethylene, reduce the ripening process and extend the shelf life of fruits.

Electrospun Fe doped TiO2 fiber photocatalyst for efficient wastewater treatment

Water pollution caused by industrial wastewater is the most critical environmental problem in the world. Synthetic dyes are commonly used in various industries such as paper, plastic, printing, leather and textile for their ability to impact color. Complex composition, high toxicity and low biodegradability of dyes make them difficult to degrade which causes a substantial negative impact on overall ecosystems. To address this issue we synthesized TiO₂ fibers photocatalyst using the combination of sol-gel and electrospinning techniques to be used in the degradation of dyes which causes water pollution. We doped Fe in TiO₂ fibers to enhance the absorption in the visible region of the solar spectrum which will also help to increase the degradation efficiency. As synthesized pristine TiO₂ fibers and Fe doped TiO₂ fibers were analyzed using different characterization techniques such as X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, UV-Visible spectroscopy, X-ray photoelectron spectroscopy. 5% Fe doped TiO₂ fibers show excellent photocatalytic degradation activity for rhodamine B (99% degradation in 120 min). It can be utilized for degradation of other dye pollutants such as methylene blue, Congo red and methyl orange. It shows good photocatalytic activity (97%) even after 5 cycles of reuse. The radical trapping experiments reveals that holes, ^•O₂^- and ^•OH has a significant contribution in the photocatalytic degradation. Due to the robust fibrous nature of 5FeTOF the process of collection of photocatalysts was simple and without loss as compared to powder photocatalysts. This justifies our selection of electrospinning method of synthesis of 5FeTOF which is also useful for large scale production.

Genetic algorithm-assisted artificial neural network modelling for remediation and recovery of Pb (II) and Cr(VI) by manganese and cobalt spinel ferrite super nanoadsorbent

MnFe₂O₄ and CoFe₂O₄ nanoparticles were hydrothermally synthesized to examine their capability in adsorption of Pb (II) and Cr (VI). The adsorbents exhibited a high rate of adsorption, reaching 90% of their adsorption capacity in less than 30 min. Furthermore, the adsorption capability of the Magnetic Nanoparticles (MNPs) was noticeably greater at initial pollutant concentrations smaller than 40 mg/L. Maximum adsorption capacity on MnFe₂O₄ and CoFe₂O₄ nanoparticles were 40 and 25.38 mg/g for Cr (VI) and 523.32 and 476.19 mg/g for Pb (II), respectively. A data-driven model of Artificial Neural Network was used for prediction of adsorption capacity at both equilibrium and non-equilibrium condition. The model parameters including the numbers of neuron (n = 7) and data portioning for training (49.5%), validation (40.5%), and testing (10%) were obtained using Genetic Algorithm. The results indicated that the model could predict the data with high accuracy (R² = 0.998). The input parameters were initial concentration, time, pH, temperature, adsorbent dosage, and other parameters that is dependent to the physico-chemical properties of ions and adsorbents' surface (ε, α₁, α₂). The mechanism involved in Cr(VI) and Pb(II) adsorption are electrostatic physisorption and a combination of ion exchange chemisorption and electrostatic physisorption, respectively. Desorption capability and adsorbent reuse capability were also examined.