Preparation of magnetic photocatalysts from TiO2, activated carbon and iron nitrate for environmental remediation

Hybrid collagen-cellulose-Fe3O4@TiO2 magnetic bio-sponges derived from animal skin waste and Kenaf fibers for wastewater remediation

Water pollution from synthetic dyes and oil spills has a significant impact on the environment and living species. Here, we developed a low-cost, environmentally friendly and easily biodegradable magnetic hybrid bio-sponge nanocomposite from renewable resources such as collagen and cellulose (Kenaf fibre cellulose-collagen, KFCC). We loaded it with magnetic bimetallic Fe3O4@TiO2 (BFT) NPs to produce a photocatalyst material (KFCC-BFT) for the treatment of colored wastewater as well as a sorbent for oil-water separation. The characterization of the bimetallic BFT NPs by XRD, HRTEM and VSM showed the deposition of TiO2 particles onto the surface of Fe3O4 with lattice interlayers spacing of 0.24 and 0.33 nm for Fe3O4 and TiO2, respectively with ferromagnetic property. The UV-vis diffuse reflectance spectra result indicated that the band gap energy of bio-sponges decreases with the increase of the bimetallic moiety. The photocatalytic efficiency of the as-prepared magnetic hybrid bio-sponge in the degradation of crystal violet dye was up to 91.2% under visible light conditions and 86.6% under direct sunlight exposure. Furthermore, the magnetic hybrid bio-sponge was used to separate motor oil from water (> 99%) and had a high oil sorption capacity of 46.1 g/g. Investigation of the recyclability and reusability performance for 9 cycles revealed that the bio-sponge had a high sorption capacity for up to 5 cycles. Our results suggest that the bio-polymer-supported BFT hybrid nanocomposite is a cost-effective and easily biodegradable photocatalyst and has great potential for real-field environmental remediation applications.

Green synthesis of magnetic activated carbon from peanut shells functionalized with TiO2 photocatalyst for Batik liquid waste treatment

The composite of magnetic activated carbon derived from peanut shells functionalized titanium dioxide (Fe3O4/TiO2/AC) has been successfully synthesized. The composite was employed to remove indigosol green and Cr(vi) under ultraviolet (UV) and visible light. In this work, the activated carbon was synthesized from a sustainable source of peanut shell by carbonization and activation method employing NaOH as the activating agent. Magnetite was prepared by chemical co-precipitation technique using FeCl3·6H2O and FeSO4·7H2O, and then, the deposition of TiO2 was performed under ultrasonic irradiation. A variety of material characterization, consisting of Fourier transform infrared, X-ray diffraction, and scanning electron microscopy-energy dispersive X-ray, was used to analyze the physicochemical properties of the composite. The effects of pH, irradiation time, and composite mass during optimization performance were investigated. The characterizations represent the dispersed TiO2 in the anatase phase with the existence of magnetic particles. The activity tests revealed the superiority of the composite for applications involving adsorption and photocatalysis under visible light source compared to UV light. It was found that Fe3O4/TiO2/AC yields the efficiency for the removal of indigosol green and Cr(vi) from Batik liquid waste of 92.91 and 76.92%, respectively.

TiO2/activated carbon synthesized by microwave-assisted heating for tetracycline photodegradation

A furfural residue-derived activated carbon (AC) supported black-TiO₂ photocatalyst was successfully prepared by ultrasonic-assisted sol-gel treatment (USG) and solvothermal treatment (ST) combined with microwave-assisted heating (MH). The prepared composites were characterized and evaluated based on the degradation of tetracycline hydrochloride (TC) under ultraviolet (UV) illumination. The average TiO₂ nanoparticle size of the as-synthesized catalysts was between 9 and 11 nm. The bandgap of TiO₂-USGM was 1.6 eV, much lower than that of other reference catalysts. Organic carbon and AC in the catalyst play positive roles in reducing the band gap (e.g. 1.6∼2.6 eV) and improving visible-light absorption. The oxygen vacancies are responsible for UV-visible absorption. Adding AC into black TiO₂ resulted in a lower degree of recombination of photogenerated electrons. Mott-Schottky plots showed that AC-containing TiO₂@AC-STM reduced the value of conduction band value from -0.59 eV to -0.24 eV, which is beneficial to photogenerated electrons. Compared with TiO₂, the Ti-O-C and Ti-C- in TiO₂@AC remarkably improved the adsorption and catalytic efficiency of TC. In a near-neutral pH environment, TiO₂@AC-STM and TiO₂@AC-USGM exhibited high removal efficiencies (88.0% and 75.7%, respectively) and degradation rates (0.0418 and 0.0302 μmol/g/s, respectively) at a catalyst load of 0.25 g/L. Notably, the catalyst can be effectively used over a wide range of pH (6-9). The solution pH after treatment was close to neutral, which is advantageous for wastewater treatment. The activation energies were found to be approximately 3.47 kJ/mol. The thermodynamic parameters showed that the photodegradation process was non-spontaneous and endothermic. Based on the trapping experiments, O₂⋅^- was mainly responsible for TC photodegradation over TiO₂@AC-STM, followed by h⁺. The TC degradation pathways and catalyst stability were also investigated. Biomass-derived carbon-supported catalysts have great potential for waste biomass utilization as green, and low-cost catalysts.

Recent Progress in Photocatalytic Removal of Environmental Pollution Hazards in Water Using Nanostructured Materials

Water pollution has become a critical issue because of the Industrial Revolution, growing populations, extended droughts, and climate change. Therefore, advanced technologies for wastewater remediation are urgently needed. Water contaminants are generally classified as microorganisms and inorganic/organic pollutants. Inorganic pollutants are toxic and some of them are carcinogenic materials, such as cadmium, arsenic, chromium, cadmium, lead, and mercury. Organic pollutants are contained in various materials, including organic dyes, pesticides, personal care products, detergents, and industrial organic wastes. Nanostructured materials could be potential candidates for photocatalytic reduction and for photodegradation of organic pollutants in wastewater since they have unique physical, chemical, and optical properties. Enhanced photocatalytic performance of nanostructured semiconductors can be achieved using numerous techniques; nanostructured semiconductors can be doped with different species, transition metals, noble metals or nonmetals, or a luminescence agent. Furthermore, another technique to enhance the photocatalytic performance of nanostructured semiconductors is doping with materials that have a narrow band gap. Nanostructure modification, surface engineering, and heterojunction/homojunction production all take significant time and effort. In this review, I report on the synthesis and characterization of nanostructured materials, and we discuss the photocatalytic performance of these nanostructured materials in reducing environmental pollutants.

Magnetic photocatalysts from δ-FeOOH and TiO2 and application in reactions for degradation of methylene blue and paracetamol with UV-C and sunlight

Water contamination is a common problem, especially considering dyes and drugs disposal. A possible and effective treatment method to remove these organic pollutants from water is photocatalytic reaction. This study aimed to improve the photocatalytic properties of TiO₂ using iron oxides (Ti/Fe composite). Different magnetic photocatalysts based on commercial TiO₂ were obtained with 30, 50, and 80% (wt./wt.) of TiO₂ supported on maghemite. X-ray diffraction with Rietveld refinement confirms the presence of γ-Fe₂O₃, α-Fe₂O₃, anatase, and rutile, as well as the relative percentages of the phases present in each photocatalyst. The magnetic properties were certified by VSM and sedimentation kinetics in the presence of a magnetic field. Besides their magnetic properties, UV-vis DRS shows that the obtained photocatalysts presented lower bandgap values when compared with TiO₂. These factors allowed the materials to absorb radiation in the visible-light region and the separation from the reaction medium by the application of magnetic field. It was observed an enhancement of photodegradation reaction of methylene blue (MB) and paracetamol (PC). For example, when the content of TiO₂ increased from 30 to 80% (wt./wt.), the efficiency increased from 58 to 99% (for MB) and 39 for 80% (for PC) under UV (λ = 254 nm). The reactions carried out with solar radiation showed 56 to 95% efficiency to discolor MB. In addition, the results of sedimentation kinetics and characterization confirmed the goals of the synthesis.

Synthesis of Oxygen Deficient TiO2 for Improved Photocatalytic Efficiency in Solar Radiation

The photocatalytic activities of TiO2 have been limited mainly to absorbing in the ultraviolet spectrum which accounts for only 5% of solar radiation. High energy band gap and electron recombination in TiO2 nanoparticles are responsible for its limitations as a photocatalyst. An oxygen deficient surface can be artificially created on the titanium oxide by zero valent nano iron through the donation of its excess electrons. A visible light active TiO2 nanoparticle was synthesized in the current investigation through simple chemical reduction using sodium boro-hydride. The physical and textural properties of the synthesized oxygen deficient TiO2 photocatalyst was measured using scanning/ transmission electron microscopy while FTIR, XRD and nitrogen sorption methods (BET) were employed for its further characterizations. Photochemical decoloration of orange II sodium dye solution in the presence of the synthesized TiO2 was measured using an UV spectrophotometer. The resulting oxygen deficient TiO2 has a lower energy band-gap, smaller pore sizes, and enhanced photo-catalytic properties. The decoloration (88%) of orange (II) sodium salt solution (pH 2) under simulated solar light was possible at 20 min. This study highlights the effect of surface oxygen defects, crystal size and energy band-gap on the photo-catalytical property of TiO2 nanoparticles as impacted by nano zero valent iron. It opens a new window in the exploitation of instability in the dopant ions for creation of a visible light active TiO2 photocatalyst.

Enhancement of photocatalytic degradation of Malachite Green using iron doped titanium dioxide loaded on oil palm empty fruit bunch-derived activated carbon

Iron-doped titanium dioxide loaded on activated carbon (Fe-TiO₂/AC) was successfully synthesized from oil palm empty fruit bunch (OPEFB) using sol-gel method. The properties of the synthesized pure TiO₂, Fe-doped TiO₂, AC, TiO₂/AC and Fe-TiO₂/AC were examined by various techniques such as field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and nitrogen adsorption-desorption analyses at 77 K. FE-SEM revealed that Fe-doped TiO₂ particles were dispersed homogeneously on the AC surface. FT-IR demonstrated high surface hydroxylation after Fe doping on TiO₂ and UV-Vis DRS showed that Fe-TiO₂/AC had the lowest band gap energy. Catalytic performance results proved that Fe dopants could restrict the recombination rate of hole and electron pairs, whereas AC support improved the Malachite Green (MG) adsorption sites and active sites of the hybrid catalyst. Photocatalytic degradation of 100 mg/L MG in the presence of 1.0 g/L 15 wt% Fe-TiO₂ incorporated with 25 wt% AC, initial solution pH of 4 and 3 mM H₂O₂ could achieve the highest removal efficiency of 97% after 45 min light irradiation. This work demonstrates a promising approach to synthesis an inexpensive and efficient Fe-TiO₂/AC for the photocatalytic degradation of organic dye.

Characteristics and Behavior of Different Catalysts Used for Water Decontamination in Photooxidation and Ozonation Processes

The objective of this study was to summarize the results obtained in a wide research project carried out for more than 15 years on the catalytic activity of different catalysts (activated carbon, metal–carbon xerogels/aerogels, iron-doped silica xerogels, ruthenium metal complexes, reduced graphene oxide-metal oxide composites, and zeolites) in the photooxidation (by using UV or solar radiation) and ozonation of water pollutants, including herbicides, naphthalenesulfonic acids, sodium para-chlorobenzoate, nitroimidazoles, tetracyclines, parabens, sulfamethazine, sodium diatrizoate, cytarabine, and surfactants. All catalysts were synthesized and then texturally, chemically, and electronically characterized using numerous experimental techniques, including N2 and CO2 adsorption, mercury porosimetry, thermogravimetric analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, diffuse reflectance UV–vis spectroscopy, photoluminescence analysis, and transmission electron microscopy. The behavior of these materials as photocatalysts and ozonation catalysts was related to their characteristics, and the catalytic mechanisms in these advanced oxidation processes were explored. Investigations were conducted into the effects on pollutant degradation, total organic carbon reduction, and water toxicity of operational variables and the presence of different chemical species in ultrapure, surface, ground, and wastewaters. Finally, a review is provided of the most recent and relevant published studies on photocatalysis and catalyzed ozonation in water treatments using similar catalysts to those examined in our project.