TiO2–Zeolite Metal Composites for Photocatalytic Degradation of Organic Pollutants in Water

TiO2 immobilized on 2D mordenite: effect of hydrolysis conditions on structural, textural, and optical characteristics of the nanocomposites

A series of novel TiO2/2D mordenite nanocomposites were synthetized by the introduction of titanium tetraethoxide (TEOT) into the interlamellar space of 2D mordenite, its subsequent hydrolysis in water or a solution of 70% ethanol in water for 6, 12, and 24 h, and calcination. The resulting TiO2/2D mordenite materials were studied by a set of complementary characterization techniques, including XRD, SEM-EDX, TGA, N2 sorption, NMR, XPS and UV-vis spectrometry. It was observed that treatment in 70% ethanol solution preserves the ordered layered structure of 2D mordenite because TEOT hydrolysis is slowed down. This, in turn, leads to higher mesoporosity after calcination due to anatase nanoparticles of about 4 nm preventing the collapse of the interlamellar space. Immobilization of TiO2 on the zeolite surface is evidenced by the formation of Si-O-Ti bonds. The bandgap width of the synthetized nanocomposites was found to be sensitive to the hydrolysis medium.

Co- and Ni-Doped TiO2 Nanoparticles Supported on Zeolite Y with Photocatalytic Properties

Zeolite Y samples with microporous and hierarchical structures containing Ti-Ni and Ti-Co oxides were obtained as active photocatalysts. Different Ti amounts (5, 10% TiO2) were supported, followed by the loading of Ni or Co oxides (5%). X-ray diffraction evidenced the presence of TiO2 as an anatase. N2 adsorption-desorption results showed type IV isotherms for hierarchical zeolite Y samples, and a combination of type IV and I isotherms for zeolite Y samples. UV-Vis diffuse reflectance spectra showed a shift in the absorption band to visible with increasing Ti loading and especially after Co and Ni addition. A significant effect of the support was evidenced for Ti and its interaction with Co/Ni species. The zeolite Y support stabilized Ti in the 4+ oxidation state while hierarchical zeolite Y support favored the formation of Ti3+ species, Ni0 and Ni2+ and the oxidation of Co to 3+ oxidation state. Photocatalytic activity, under UV and visible light irradiation, was evaluated by the degradation of amoxicillin, used as a model test. The photocatalytic mechanism was investigated using ethanol, p-benzoquinone and KI as ·OH and ·O2- radicals and hole (h+) scavengers. The best results were obtained for the immobilized Ni-Ti species on the hierarchical zeolite Y support.

Performance of TiO2-Based Tubular Membranes in the Photocatalytic Degradation of Organic Compounds

This work presents the photocatalytic degradation of organic pollutants in water with TiO₂ and TiO₂/Ag membranes prepared by immobilising photocatalysts on ceramic porous tubular supports. The permeation capacity of TiO₂ and TiO₂/Ag membranes was checked before the photocatalytic application, showing high water fluxes (≈758 and 690 L m^-2 h^-1 bar^-1, respectively) and <2% rejection against the model pollutants sodium dodecylbenzene sulfonate (DBS) and dichloroacetic acid (DCA). When the membranes were submerged in the aqueous solutions and irradiated with UV-A LEDs, the photocatalytic performance factors for the degradation of DCA were similar to those obtained with suspended TiO₂ particles (1.1-fold and 1.2-fold increase, respectively). However, when the aqueous solution permeated through the pores of the photocatalytic membrane, the performance factors and kinetics were two-fold higher than for the submerged membranes, mostly due to the enhanced contact between the pollutants and the membranes photocatalytic sites where reactive species were generated. These results confirm the advantages of working in a flow-through mode with submerged photocatalytic membranes for the treatment of water polluted with persistent organic molecules, thanks to the reduction in the mass transfer limitations.

CuNi Alloy NPs Anchored on Electrospun PVDF-HFP NFs Catalyst for H2 Production from Sodium Borohydride

Non-noble Cu_xNi_1-x (x = 0, 0.1, 0,2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1) alloy nanoparticles supported on poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) nanofibers (NFs) are successfully fabricated. The fabrication process is executed through an electrospinning technique and in situ reduction in Cu²⁺ and Ni²⁺ salts. The as-synthesized catalysts are characterized using standard physiochemical techniques. They demonstrate the formation of bimetallic NiCu alloy supported on PVDF-HFP. The introduced bimetals show better catalytic activity for sodium borohydride (SBH) hydrolysis to produce H₂, as compared to monometallic counterparts. The Cu_0.7 Ni_0.3/PVDF-HFP catalyst possesses the best catalytic performance in SBH hydrolysis as compared to the others bimetallic formulations. The kinetics studies indicate that the reaction is zero order and first order with respect to SBH concentration and catalyst amount, respectively. Furthermore, low activation energy (Ea = 27.81 kJ/mol) for the hydrolysis process of SBH solution is obtained. The excellent catalytic activity is regarded as the synergistic effects between Ni and Cu resulting from geometric effects over electronic effects and uniform distribution of bimetallic NPs. Furthermore, the catalyst displays a satisfying stability for five cycles for SBH hydrolysis. The activity has retained 93% from the initial activity. The introduced catalyst has broad prospects for commercial applications because of easy fabrication and lability.

Shedding light on the performance of magnetically recoverable TiO2/Fe3O4/rGO-5 photocatalyst. Degradation of S-metolachlor as case study

Recalcitrant contaminants are not usually removed in conventional wastewater treatment plants. Therefore, they are transferred to the water resources that receive treated wastewaters and their presence can cause health and environmental issues. Herbicides are among these compounds. In particular, S-metolachlor (MTLC) is specifically of high concern because its molecule incorporates a chlorine atom that contributes to its toxicity. For its removal, a magnetically recoverable photocatalyst, TiO₂/Fe₃O₄/rGO-5, was synthesised following a hydrothermal method. The performance of TiO₂/Fe₃O₄/rGO-5 has been experimentally assessed and compared to TiO₂ and TiO₂/rGO-5 catalysts. A characterisation of the materials properties was carried out including adsorption isotherms of MTLC that provided the maximum adsorption capacity of the materials (q_m), being 140.85 ± 5.14 mg g^-1 for TiO₂/Fe₃O₄/rGO-5. Furthermore, the ternary composite exhibited good recoverability from liquid media after four consecutive cycles thanks to its magnetic character (magnetic saturation of 13.85 emu g^-1). Photocatalytic degradation of MTLC started after a dark adsorption step following first order kinetics (0.0197 ± 1.2 × 10^-4 min^-1 for the degradation of 100 mg L^-1 of MTLC with 0.5 g L^-1 of TiO₂/Fe₃O₄/rGO-5) similar to the rate of appearance of chloride in solution; after total removal of the solubilized MTLC the chloride concentration in the solution continued increasing with zero-th order kinetics up to the value corresponding to the total MTLC concentration. This second step in the chloride formation was attributed to the degradation of adsorbed MTLC. Specific experiments in the presence of scavengers of reactive oxygen species (ROS) were carried out shedding light on the degradation mechanisms. It was concluded the predominant role of free hydroxyl radicals in the photocatalytic degradation in all the investigated materials, whereas the presence of rGO in the composite photocatalysts improved their electronic conductivity, enhancing the activity of superoxide radicals. The results of this work provide important information for further development of photocatalysis.

Sustainable approaches towards green synthesis of TiO2 nanomaterials and their applications in photo-catalysis mediated sensingtomonitor environmental pollutions

Nanomaterials are gaining enormous interests owing to their novel applications that have been explored nearly in every field of our contemporary society. In this scenario, preparations of nanomaterials following green routes have attracted widespread attention in terms of sustainable, reliable and environmentally friendly practice to produce diverse nanostructures. In this review, we summarized the fundamental processes and mechanisms of green synthesis approaches of TiO₂ NPs. We explore the role of plants and microbes as natural bioresources to prepare TiO₂ NPs. Particularly, focused have been made to explore the potential of TiO₂ based nanomaterials to design variety of sensing platforms by exploiting the photo-catalysis efficiency under the influence of light source. Such types of sensing can of massive importance to monitor the environmental pollutions and thereby to invent advanced strategies to remediate hazardous pollutants to offer clean environment.

Oxide coatings with immobilized Ce-ZSM5 as visible light photocatalysts

The preparation and properties of oxide coatings with immobilized ZSM-5 zeolite obtained by plasma electrolytic oxidation on aluminum support are investigated and discussed. Pure and Ce-exchanged ZSM-5 are immobilized on aluminum support from silicate-based electrolyte in ultra-low duty cycle pulsed direct current conditions. Obtained composite coatings are characterized with respect to their morphology, phase and chemical composition, as well as photocatalytic activity and anti-corrosion properties. All mentioned properties of obtained coatings are dependent on processing time. Coatings with Ce-exchanged ZSM-5 show higher photocatalytic activity and more effective corrosion protection than those with pure ZSM-5. The highest photocatalytic activity is observed for coatings processed for 30 minutes. It is suggested that surface morphology, Ce-content and number of defects influence the photocatalytic activity of composite coatings.

Microcystis@TiO2 Nanoparticles for Photocatalytic Reduction Reactions: Nitrogen Fixation and Hydrogen Evolution

Solar-driven photocatalysis has been known as one of the most potential technologies to tackle the energy shortage and environmental pollution issues. Utilizing bio-pollutants to prepare functional materials has been considered as a green option. Herein, we used Microcystis aeruginosa as a bio-template to fabricate a Microcystis@TiO2 photocatalyst using a calcination method. The as-prepared Microcystis@TiO2 showed prominent ability as well as favorable stability for photocatalytic reduction reactions including hydrogen evolution and nitrogen fixation. Under light illumination, Microcystis@TiO2 calcined at 550 °C exhibited optimal photo-reduced activity among all samples, with the highest hydrogen evolution (1.36 mmol·g−1·h−1) and ammonia generation rates (0.97 mmol·g−1·h−1). This work provides a feasible approach to prepare functional materials from disposed pollutants.