This article presents an overview of the reports on the doping of TiO₂ with carbon, nitrogen, and sulfur, including single, co-, and tri-doping. A comparison of the properties of the photocatalysts synthesized from various precursors of TiO₂ and C, N, or S dopants is summarized. Selected methods of synthesis of the non-metal doped TiO₂ are also described. Furthermore, the influence of the preparation conditions on the doping mode (interstitial or substitutional) with reference to various types of the modified TiO₂ is summarized. The mechanisms of photocatalysis for the different modes of the non-metal doping are also discussed. Moreover, selected applications of the non-metal doped TiO₂ photocatalysts are shown, including the removal of organic compounds from water/wastewater, air purification, production of hydrogen, lithium storage, inactivation of bacteria, or carbon dioxide reduction.

This paper presents an overview of recent reports on photocatalytic membrane reactors (PMRs) in organic synthesis as well as water and wastewater treatment. A brief introduction to slurry PMRs and the systems equipped with photocatalytic membranes (PMs) is given. The methods of PM production are also presented. Moreover, the process parameters affecting the performance of PMRs are characterized. The applications of PMRs in organic synthesis are discussed, including photocatalytic conversion of CO₂, synthesis of KA oil by photocatalytic oxidation, conversion of acetophenone to phenylethanol, synthesis of vanillin and phenol, as well as hydrogen production. Furthermore, the configurations and applications of PMRs for removal of organic contaminants from model solutions, natural water and municipal or industrial wastewater are described. It was concluded that PMRs represent a promising green technology; however, before the application in industry, additional studies are still required. These should be aimed at improvement of process efficiency, mainly by development and application of visible light active photocatalysts and novel membranes resistant to the harsh conditions prevailing in these systems.

Silver nanoparticles (NPs) are effective antibacterial agents; however, aggregation of NPs and uncontrolled release of Ag⁺ affect their efficiency and may pose a risk to the environment. To overcome these disadvantages, immobilization of Ag onto titanate nanotubes (TNTs) was investigated. This paper describes the physicochemical and antibacterial properties of silver incorporated titanate nanotubes (Ag/TNTs) prepared using five procedures and containing different Ag amounts (0.11–30.85 wt.%). The methods were (i) sol-gel followed by a hydrothermal process; (ii) photodeposition under ambient conditions; (iii) photodeposition under an inert atmosphere; (iv) NaBH₄ reduction; and (v) electroless deposition after activation of TNTs with Sn²⁺. Depending on the synthesis procedure, the presence of metallic Ag NPs, AgO or AgCl was observed. The electroless method led to an additional deposition of SnO₂ NPs. The antibacterial properties of Ag/TNTs were analyzed as a function of Ag content and released against Escherichia coli and Staphylococcus epidermidis. The best bactericidal properties exhibited Ag/TNTs prepared through the photodeposition process due to the higher interaction of exposed Ag NPs with bacteria. An increase of Ag loading resulted in improvement of antibacterial activity of Ag/TNTs although no direct correlation between silver content or release and inhibition of bacterial growth was found.

Ultrafiltration polyethersulfone (PES) membranes were prepared by wet phase inversion. Commercial halloysite nanotubes (HNTs) in the quantities of 0.5 wt% vs. PES (15 wt%) were introduced into the casting solution containing the polymer and different solvents: N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), or 1-methyl-2-pyrrolidinone (NMP). The type of solvent influenced the membranes’ morphology and topography, as well as permeability, separation characteristics, and antifouling and antibacterial properties. The membranes prepared using DMA exhibited the loosest cross-section structure with the thinnest skin and the roughest surface, while the densest and smoothest were the DMF-based membranes. The advanced contact angles were visibly lower in the case of the membranes prepared using DMF compared to the other solvents. The highest water permeability was observed for the DMA-based membranes, however, the most significant effect of the modification with HNTs was found for the NMP-based series. Regardless of the solvent, the introduction of HNTs resulted in an improvement of the separation properties of membranes. A noticeable enhancement of antifouling performance upon application of HNTs was found only in the case of DMF-based membranes. The study of the antibacterial properties showed that the increase in surface roughness had a positive effect on the inhibition of E. coli growth.

This paper describes the investigations on the possibilities of treatment of wastewater generated in an industrial laundry with application of a combined biological-photooxidation- membrane system aimed at water recycle and reuse. The two treatment schemes were compared: 1) scheme A consisting of a treatment in a moving bed biological reactor (MBBR) followed by microfiltration (MF) and nanofiltration (NF), and 2) scheme B comprising MBBR followed by oxidation by photolysis enhanced with in situ generated O₃ (UV/O₃) after which MF and NF were applied. The removal efficiency in MBBR reached 95–97% for the biochemical oxygen demand; 90–93% for the chemical oxygen demand and 89–99% for an anionic and a nonionic surfactants. The application of UV/O₃ system allowed to decrease the content of the total organic carbon by 68% after 36 h of operation with a mineralization rate of 0.36 mg/L·h. Due to UV/O₃ pretreatment, a significant mitigation of membrane fouling in the case of both MF and NF processes was achieved. The MF permeate flux in the system B was over two times higher compared to that in the system A. Based on the obtained results it was concluded that the laundry wastewater pretreated in the MBBR-UV/O₃-MF-NF system could be recycled to any stage of the laundry process.

In the presented studies it was hypothesized that the modification of a polymeric membrane with a pore former and a hybrid nanomaterial composed of titanate nanotubes with deposited Ag nanoparticles (Ag-TNTs NPs) can protect the membrane from the microbial growth, and thus enhance its resistance to biofouling. Polyethersulfone (PES) membranes were prepared by the wet phase inversion, and polyvinylpyrrolidone (PVP) and poly(ethylene glycol) (PEG) were used as pore formers. The membranes were characterized in terms of morphology, topography, permeability, separation characteristics, and anti-(bio)fouling properties as well as antibacterial activity. The membranes modified with porogens and Ag-TNTs revealed improved hydrophilicity and water permeability compared to the unmodified membrane, from 58 to 66%. Moreover, the improvement in rejection of model dextrans and PEG upon application of the NPs was found. However, the use of PVP or PEG had a negative influence on the resistance to fouling by bovine serum albumin, i.e., ca. 35% of decline of permeate flux was noticed after 2 h of ultrafiltration of BSA. On the contrary, both porogens and NPs contributed to biofouling mitigation. The introduction of pore formers had a positive effect on the inhibition of Escherichia coli growth by the membrane containing Ag-TNTs. The log reduction of bacteria varied from 3.17 to 3.3 in case of stirred and filtration system.