Visible-light-driven photocatalytic removal of PPCPs using magnetically separable bismuth oxybromo-iodide solid solutions: Mechanisms, pathways, and reusability in real sewage

The environmental sources of benzophenones: Distribution, pretreatment, analysis and removal techniques

Benzophenones (BPs) have wide practical applications in real human life due to its presence in personal care products, UV-filters, drugs, food packaging bags, etc. It enters the wastewater by daily routine activities such as showering, impacting the whole aquatic system, then posing a threat to human health. Due to this fact, the monitoring and removal of BPs in the environment is quite important. In the past decade, various novel analytical and removal techniques have been developed for the determination of BPs in environmental samples including wastewater, municipal landfill leachate, sewage sludge, and aquatic plants. This review provides a critical summary and comparison of the available cutting-edge pretreatment, determination and removal techniques of BPs in environment. It also focuses on novel materials and techniques in keeping with the concept of "green chemistry", and describes on challenges associated with the analysis of BPs, removal technologies, suggesting future development strategies.

Visible-Light-Active Iodide-Doped BiOBr Coatings for Sustainable Infrastructure

The search for efficient materials for sustainable infrastructure is an urgent challenge toward potential negative emission technologies and the global environmental crisis. Pleasant, efficient sunlight-activated coatings for applications in self-cleaning windows are sought in the glass industry, particularly those produced from scalable technologies. The current work presents visible-light-active iodide-doped BiOBr thin films fabricated using aerosol-assisted chemical vapor deposition. The impact of dopant concentration on the structural, morphological, and optical properties was studied systematically. The photocatalytic properties of the parent materials and as-deposited doped films were evaluated using the smart ink test. An optimized material was identified as containing 2.7 atom % iodide dopant. Insight into the photocatalytic behavior of these coatings was gathered from photoluminescence and photoelectrochemical studies. The optimum photocatalytic performance could be explained from a balance between photon absorption, charge generation, carrier separation, and charge transport properties under 450 nm irradiation. This optimized iodide-doped BiOBr coating is an excellent candidate for the photodegradation of volatile organic pollutants, with potential applications in self-cleaning windows and other surfaces.

Solar-driven photocatalytic chlorine activation for the simultaneous degradation of pharmaceuticals and personal care products and the inactivation of Escherichia coli in drinking water

Removal of pharmaceuticals and personal care products (PPCPs) is often inefficient during conventional water treatment, posing threats to human health. Herein, we have developed a novel solar/TiO2/chlorine system upgraded from chlorine disinfection for the simultaneous degradation of PPCPs and the inactivation of Escherichia coli from drinking water. The addition of 100 μM of chlorine to the photocatalytic process considerably enhanced the degradation efficiency of PPCPs and demonstrated excellent disinfecting abilities, as confirmed by a 4.7 × increase in the carbamazepine degradation rate constant coupled with a 3.2-log (99.94%) reduction of E. coli cells within 1 min. Photoinduced charge pairs (hVB+ and eCB-) were identified for reactive species generation, and HO• and ClO• were the primary contributors to PPCPs degradation. The process exhibited satisfactory carbamazepine degradation efficiency in different water matrices and the cycling tests showed the TiO2 photocatalyst to be highly stable and reusable. Overall, our solar/TiO2/chlorine system is a potentially effective alternative to conventional drinking water treatment using chlorination.

Effective photocatalytic degradation of sulfamethoxazole using tunable CaCu3Ti4O7 perovskite

Sulfamethoxazole (SMX) is largely prescribed for bacterial infections but raises a major concern over generation of antibiotic-resistant bacteria in the environment. This study employed various perovskite-type photocatalysts, made by two-step synthesis procedures, to remove SMX. The as-synthesized CaCu₃Ti₄O₇ (CCTO) perovskites were characterized by XRD, SEM-EDX, and DLS. Complete degradation (∼99%; k_obs = 0.0279 min^-1) of SMX was recorded under UV-light irradiation for 90 min in the presence of CCTO. SMX removal rate was investigated under various reaction conditions including pH, catalyst dose, electrolyte (NaCl and NaBr). The astonishing rate of SMX removal (k_obs = 0.0614 min^-1) was observed with the addition of 50 mM NaBr electrolytes in the reaction, which might imply that the appearance of halogen reactive species. CCTO-MS particles were aggregated in traces when the electrolytes concentration increases, resulting in reduced rate of SMX. The SMX concentration abatement and the formation of possible intermediates during photocatalytic reaction were analyzed. The upshot of this study reveals that the inexpensive and environmentally benign CCTO perovskite photocatalyst could be applied for the treatments of emerging contaminants in the future.

Exploring the activation pathway of photo-induced electrons in facets-dependent I-doped BiOCl nanosheets for PCPNa degradation

Electrons can degrade pentachlorphenate sodium (PCPNa) directly or activate molecular oxygen to produce·O2-and ·OH for its degradation. However, less work has been performed to control such two kinds of reaction pathway by modifying BiOCl. Herein, we firstly regulated the reaction pathway between electrons and PCPNa by adjusting the amount of surface oxygen vacancies (OVs) and surface adsorbed hydroxyl groups in I^-doped BiOCl exposed with different facets. OVs on (001) facets-exposed I^-doped BiOCl enabled large amount of PCPNa to adsorb on its surface and facilitated the direct reaction between electrons and PCPNa. In contrary, more surface adsorbed hydroxyl groups and oxygen on (010) facets-exposed I^-doped BiOCl can retard the direct reaction between electrons and PCPNa via lowering the adsorption of PCPNa and increasing the activation of molecular oxygen by electrons. Although more·O2-and ·OH generated in I^-doped (010)-facets exposed BiOCl, I^-doped (001)-facets exposed BiOCl exhibited better photocatalytic activity. We proposed that the direct reaction between electrons and PCPNa can enhance the utilization efficiency of photogenerated electrons and improve photocatalytic degradation efficiency of PCPNa.

Pharmaceutical and Personal Care Products in Different Matrices: Occurrence, Pathways, and Treatment Processes

The procedures for analyzing pharmaceuticals and personal care products (PPCPs) are typically tedious and expensive and thus, it is necessary to synthesize all available information from previously conducted research. An extensive collection of PPCP data from the published literature was compiled to determine the occurrence, pathways, and the effectiveness of current treatment technologies for the removal of PPCPs in water and wastewater. Approximately 90% of the compiled published papers originated from Asia, Europe, and the North American regions. The incomplete removal of PPCPs in different water and wastewater treatment processes was widely reported, thus resulting in the occurrence of PPCP compounds in various environmental compartments. Caffeine, carbamazepine, diclofenac, ibuprofen, triclosan, and triclocarban were among the most commonly reported compounds detected in water and solid matrices. Trace concentrations of PPCPs were also detected on plants and animal tissues, indicating the bioaccumulative properties of some PPCP compounds. A significant lack of studies regarding the presence of PPCPs in animal and plant samples was identified in the review. Furthermore, there were still knowledge gaps on the ecotoxicity, sub-lethal effects, and effective treatment processes for PPCPs. The knowledge gaps identified in this study can be used to devise a more effective research paradigm and guidelines for PPCP management.

Photodegradation of Pharmaceutical and Personal Care Products (PPCPs) and Antibacterial Activity in Water by Transition Metals

The intensity of emerging pollutants such as pharmaceuticals and personal care products (PPCPs) in the aquatic and terrestrial environment is a major source of concern to researchers. The current conventional methods of wastewater treatment plants are considered not efficient enough in the complete removal of the recalcitrant contaminants from water. The use of modified transition metals in visible responsive synthesis to degrade PPCPs and other pollutants (organic and inorganic) is considered as a developing green chemistry and sustainable technology. Hence, this review presents the state-of-the-art discussion on the novel photodegradation of PPCPs, and antibacterial activities of transition metal-modified magnetite materials for wastewater treatment, and suggested directions for the future. Transition metal-modified magnetite nanostructured photocatalysis is identified as one of the best candidates employed in advanced oxidation processes (AOPs) for wastewater treatment and has been found to efficiently destroy bacterial spores and effectively remove recalcitrant pollutants in water. Therefore, this article hopes to contribute scientific knowledge along with existing ones on advanced mechanisms and technology used in wastewater treatment.

Simultaneous photocatalytic degradation of ibuprofen and H2 evolution over Au/sheaf-like TiO2 mesocrystals

Considerable effort has been devoted to the efficient degradation of pharmaceuticals and personal care products (PPCPs), while the chemical energy in these processes has been widely overlooked. In this study, we demonstrated the simultaneous hydrogen production and ibuprofen degradation through heterogeneous photocatalysis. By anchoring Au nanoparticles (NPs) on the (101) surface of sheaf-like TiO₂ mesocrystals with [001] orientation, efficient charge separation is achieved, which is essential for the photocatalytic redox reactions. XPS analysis showed that the binding energies of Ti 2p and O 1s indicated no shift after Au addition. Peaks observed at 81.8 and 85.5 eV due to Au 4f_7/2 and Au 4f_5/2 of metallic gold on the surface of Au/meso-TiO₂, confirmed the formation of Au NPs. The as-synthesized anatase TiO₂ mesocrystals are composed of small nanocrystals with a size of 8 nm and exhibit the uniform sheaf-like morphology along [001] orientation. As expected, the 1 wt% Au/TiO₂ mesocrystals shows the largest photocurrent density, highest H₂-evolution rate, and fastest photodegradation rate of ibuprofen under simulated sunlight irradiation among all the studied catalyst. Furthermore, the effect of solution pH, common anions (Cl^-, NO₃^-, and SO₄^2-) and cations (Na⁺, K⁺, and Ca²⁺) on photocatalytic H₂ evolution and degradation of ibuprofen were individually investigated and discussed. A mechanism for the simultaneous photocatalytic hydrogen generation and degradation of ibuprofen has also been proposed. This work opens up new opportunities for the development of energy efficient techniques for PPCPs degradation.

Optimization and characterization of zeolite-titanate for ibuprofen elimination by sonication/hydrogen peroxide/ultraviolet activity

In this study, a photo-catalyst of titanium oxide was coated on zeolite by the sol-gel method. The generation of the zeolite-titanate photo-catalyst was optimized at conditions of calcination temperature (300, 350, 400 and 500 °C), calcination time (1, 2, 3, and 4 h), and titanate content (0, 2, 4, 6, and 8 mL). The catalyst was used for 'Sonication/UV/H₂O₂″ activity and finally, eliminating ibuprofen. Physicochemical properties of the as-built photo-catalysts for all optimized conditions were determined using FESEM-EDX-mapping, BET, FTIR, and XRD. The highest percentage of ibuprofen removal (98.9%) was obtained at conditions of zeolite to titanium ratio of 1 g: 2 mL, time in the furnace of 1 h, and temperature of the furnace of 350 °C. The optimum photo-catalytic (namely, Cat-350-1-2) had a surface area value of 39 m²/g and a crystalline size of 4.9 nm. The surface area for all photo-catalysts increased after being used for ibuprofen removal, possibly due to ultrasonic waves. The presence of Ti-O, benzene ring, O-Al-O, O-Si-O, C-H, and O-H in the photo-catalysts structure were confirmed. Growing the calcination time resulted in an increase in the crystallinity of titanium dioxide in the photo-catalysts and, ultimately a reduction in the ibuprofen removal. The consumed energy by the developed system was calculated for the presence (0.094 kJ/g) and absence (17.5 kJ/g) of the ultrasonic wave. The degradation pathway and reaction kinetic are also explored and proposed. The results showed that the ultrasonic-UV-activated H₂O₂-based technique can be applied as an alternative method for ibuprofen removal from aqueous media.

Recent developments and challenges in practical application of visible-light-driven TiO2-based heterojunctions for PPCP degradation: A critical review

The ability of the TiO₂-based photocatalysis process to mineralize organic pollutants has attracted attention worldwide for the degradation of recalcitrant pharmaceuticals and personal care products (PPCPs). Nevertheless, (1) the limited exploitation of the solar spectrum, i.e., activation under UV light (only 2-3% of solar spectrum), and (2) the high recombination rate of photo-generated charge carriers, i.e., electrons and holes, have limited its application which can, however, be improved by developing a TiO₂-based heterojunction. The objective of this critical review paper is to discuss the recent developments (2009-2019) in visible-light-driven (VLD) TiO₂-based heterojunctions for PPCP degradation and their degradation mechanisms. Compared to the conventional heterojunctions, Schottky and Z-scheme heterojunctions, which are non-conventional heterojunctions, are found to be more effective for PPCP degradation due to their more efficient separation of charge carriers and the occurrence of redox reactions at a relatively higher redox potential. Furthermore, the enhancement strategies for the development of a VLD TiO₂-based heterojunction are also explored which can be achieved by selecting the (1) highly photocatalytically active {001} facet of anatase TiO₂, (2) synthesis methods governing the structural changes at the junction interface, and (3) heterojunction components which can efficiently generate the powerful •OH radicals. The challenges in practical applications are also discussed which include factors, viz., cost reduction, recycling, stability, byproducts analysis, evaluation of the environmental effectiveness, and reactor design and scale-up of the VLD TiO₂-based heterojunctions. Accordingly, the prospects of VLD TiO₂-based heterojunctions for PPCP degradation in real environmental applications are discussed.

Unravelling mechanistic reasons for differences in performance of different Ti- and Bi-based magnetic photocatalysts in photocatalytic degradation of PPCPs

Despite numerous developments in the field of heterogeneous photocatalysis, particularly its environmental applications, there remain fundamental uncertainties regarding the key properties which primarily govern the performance of a photocatalyst. In this study, four visible-light-driven magnetic photocatalysts, viz., Ag/Fe,N-TiO₂/Fe₃O₄@SiO₂, g-C₃N₄/TiO₂/Fe₃O₄@SiO₂, BiOBr/Fe₃O₄@SiO₂, and BiOBr_0.9I_0.1/Fe₃O₄@SiO₂, were synthesized and comparatively studied in terms of their material characteristics, charge transfer efficiency, and photocatalytic performance in the degradation of two model pharmaceuticals and personal care products (PPCPs), ibuprofen and benzophenone-3. Amongst the tested photocatalysts, the g-C₃N₄/TiO₂/Fe₃O₄@SiO₂ exhibited the fastest degradation kinetics for both the PPCPs. Property-performance relationships were evaluated in which the dependence of the photocatalytic performance on various adsorption-related, electronic band-structure-related, reactive species-related, and charge carriers-related properties was examined. The strongest performance relationship was found to be with photocurrent density-an indicator of charge transfer efficiency-for both PPCPs, indicating its influential role in governing the photocatalytic performance. The findings unfold a potential research direction towards exploration of factors which can enhance the charge transfer efficiency, thereby possibly enabling the rational design of highly efficient photocatalysts for PPCPs removal.