Mechanism investigation on the enhanced photocatalytic oxidation of nonylphenol on hydrophobic TiO2 nanotubes

Recent advances in advanced oxidation processes (AOPs) for the treatment of nitro- and alkyl-phenolic compounds

The presence of phenolic compounds in the aquatic environment has posed severe risks due to their toxicity. Among the phenolic families, nitro- and alkyl-phenolic compounds have been categorized as precedence contaminants by the United States Environmental Protection Agency (US EPA). Therefore, efficient treatment methods for wastewater containing nitro- and alkyl-phenolic compounds are urgently needed. Due to the advantages of creating reactive species and generating efficient degradation of hazardous contaminants in wastewater, advanced oxidation processes (AOPs) are well-known in the field of treating toxic contaminants. In this review paper, the recent directions in AOPs, catalysts, mechanisms, and kinetics of AOPs are comprehensively reviewed. Furthermore, the conclusion summarizes the research findings, future prospects, and opportunities for this study. The main direction of AOPs lies on the optimization of catalyst and operating parameters, with industrial applications remain as the main challenge. This review article is expected to present a summary and in-depth understanding of AOPs development; and thus, inspiring scientists to accelerate the evolution of AOPs in industrial applications.

Toxicity alleviation and metabolism enhancement of nonylphenol in green algae Dictyosphaerium sp. by NaHCO3

Nonylphenol (NP) toxicity limits the improvements in its algal remediation efficiency. This study comprehensively investigated the performance and mechanism of NaHCO₃-driving effects on NP-exposed algae. The results showed that NaHCO₃ enhanced algal resistance to NP and the corresponding EC₅₀ values increased 1.31-4.25 times. Further, the toxicological effects of NP reduced with increasing pyrenoid volume and chlorophyll and carotenoids production, and decreasing cellular damage degree. Moreover, the concentration of extracellular polymeric substances was enhanced and more NP adsorption sites were formed. Consistently, RNA-seq demonstrated significant expression alterations in genes related to energy metabolism, cellular synthesis, photosynthesis, and carbon fixation. Besides, NP biodegradation rate was increased by 15.2 % and 11.1 % in the 1, and 4 mg/L NP treatments, respectively. Identification of degradation intermediates and their toxicity via Ecological Structure Activity Relationship program showed that NaHCO₃ accelerated sequential α-C removal from NP in algae with faster generation of less toxic metabolites, namely, 4-ethylphenol, 4-cresol and 4-hydroxybenzoic acid. This study provides new insights into the role of NaHCO₃ in toxicity alleviation and metabolism enhancement of NP in algae and can assist NP bioremediation efforts in aquatic environment.

Synthesis of Ce0.1La0.9MnO3 Perovskite for Degradation of Endocrine-Disrupting Chemicals under Visible Photons

The UN Environmental Protection Agency has recognized 4-n-Nonylphenol (NP) and bisphenol A (BPA) as among the most hazardous chemicals, and it is essential to minimize their concentrations in the wastewater stream. These industrial chemicals have been witnessed to cause endocrine disruption. This report describes the straightforward hydrothermal approach adopted to produce Ce0.1La0.9MnO3 (CLMO) perovskite’s structure. Several physiochemical characterization approaches were performed to understand the Ce0.1La0.9MnO3 (CLMO) perovskite crystalline phase, element composition, optical properties, microscopic topography, and molecular oxidation state. Here, applying visible photon irradiation, the photocatalytic capability of these CLMO nanostructures was evaluated for the elimination of NP and BPA contaminants. To optimize the reaction kinetics, the photodegradation of NP and BPA pollutants on CLMO, perovskite was studied as a specification of pH, catalyst dosage, and initial pollutant concentration. Correspondingly, 92% and 94% of NP and BPA pollutants are degraded over CLMO surfaces within 120 and 240 min, respectively. Since NP and BPA pollutants have apparent rate constants of 0.0226 min−1 and 0.0278 min−1, respectively, they can be satisfactorily fitted by pseudo-first-order kinetics. The decomposition of NP and BPA contaminants is further evidenced by performing FT-IR analysis. Owing to its outstanding photocatalytic execution and simplistic separation, these outcomes suggest that CLMO is an intriguing catalyst for the efficacious removal of NP and BPA toxicants from the aqueous phase. This is pertinent for the treatment of endocrine-disrupting substances in bioremediation.

Integrated process approach for degradation of p-cresol pollutant under photocatalytic reactor using activated carbon/TiO2 nanocomposite: application in wastewater treatment

Over the years, biodegradation has been an effective technique for waste water treatment; however, it has its own limitations. In order to achieve a higher degradation efficacy, integrated processes are being focus in this area. Therefore, the present study is targeted towards the coupling of biodegradation and photocatalytic degradation of p-cresol. The biodegradation of p-cresol was performed via lab isolate Serratia marcescens ABHI001. The obtained results confirmed that ~85% degradation of p-cresol was accomplished using Serratia marcescens ABHI001 strain in 18 h. Consequently, degradation of remaining residue (remaining p-cresol concentration initially used) was also examined in a batch reactor using activated carbon-TiO₂ nanocomposite (AC/TiO₂-NC) as a catalyst under the exposure of UV radiation. The AC/TiO₂-NC was processed via sol-gel technique and characterized by various techniques, namely Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transformed infrared spectroscopy (FT-IR). The investigation allowed p-cresol degradation further augment up to ~96% with the help of spectrophotometer trailed by high performance liquid chromatography (HPLC). This study demonstrates that integrated process (biodegradation-photodegradation) is the cost-effective bioremediation process to overcome such kinds of pollutant issues.

Zinc Oxide Nanoparticles and Their Application in Adsorption of Toxic Dye from Aqueous Solution

Dye waste is one of the most serious types of pollution in natural water bodies, since its presence can be easily detected by the naked eye, and it is not easily biodegradable. In this study, zinc oxide nanoparticles (ZnO-NPs) were generated using a chemical reduction approach involving the zinc nitrate procedure. Fourier transform infrared (FTIR), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and UV-vis techniques were used to analyse the surface of ZnO-NPs. The results indicate the creation of ZnO-NPs with a surface area of 95.83 m2 g−1 and a pore volume of 0.058 cm3 g−1, as well as an average pore size of 1.22 nm. In addition, the ZnO-NPs were used as an adsorbent for the removal of Ismate violet 2R (IV2R) dye from aqueous solutions under various conditions (dye concentration, pH, contact time, temperature, and adsorbent dosage) using a batch adsorption technique. Furthermore, FTIR and SEM examinations performed before and after the adsorption process indicated that the surface functionalisation and shape of the ZnO-NP nanocomposites changed significantly. A batch adsorption analysis was used to examine the extent to which operating parameters, the equilibrium isotherm, adsorption kinetics, and thermodynamics affected the results. The results of the batch technique revealed that the best results were obtained in the treatment with 0.04 g of ZnO-NP nanoparticles at 30 °C and pH 2 with an initial dye concentration of 10 mg L−1, which removed 91.5% and 65.6% of dye from synthetic and textile industry effluents, respectively. Additionally, six adsorption isotherm models were investigated by mathematical modelling and were validated for the adsorption process, and error function equations were applied to the isotherm model results in order to find the best-fit isotherm model. Likewise, the pseudo-second-order kinetic model fit well. A thermodynamic study revealed that IV2R adsorption on ZnO-NPs is a spontaneous, endothermic, and feasible sorption process. Finally, the synthesised nanocomposites prove to be excellent candidates for IV2R removal from water and real wastewater systems.

Oxidation of Toluene by Ozone over Surface-Modified γ-Al2O3: Effect of Ag Addition

In this study, the ability of ozone to oxidise toluene present in low levels into CO and CO2 was studied. The catalytic ozonation of toluene was carried out in a micro-fixed bed reactor. The oxidation was done in two steps: toluene adsorption on the catalyst followed by sequential ozone desorption. Toluene breakdown by ozone at low temperature and atmospheric pressure was achieved using γ-Al2O3 supported transition metal oxides impregnated with a reduced noble metal. The catalyst Ag–CoOx/γ-Al2O3 efficiently oxidised and transformed toluene into products (52.4% COx yield). This catalyst has a high surface area, more acidic sites, and lattice oxygens for better toluene oxidation. The addition of Ag to the CoOx/γ-Al2O3 catalyst surface improved toluene adsorption on the catalyst surface, resulting in improved product yield, selectivity, and carbon balance.

Enhancing catalytic ozonation activity of MCM-41 via one-step incorporating fluorine and iron: The interfacial reaction induced by hydrophobic sites and Lewis acid sites

Fe-MCM-41 had been widely used as ozonation catalyst, however, the existence of large amount of hydrophilic silanol hindered its interfacial reaction with O₃ and pollutants. To solve this problem, F-Fe-MCM-41 was synthesized by co-doping F and Fe into the framework of MCM-41 to replace silanol with Si-F groups through a one-step hydrothermal method. F introduced hydrophobic sites which contributed to more ibuprofen (IBP) chemisorption on the surface of F-Fe-MCM-41. Moreover, doping F also enhanced the acidity, which accelerated O₃ decomposition into •OH. F-Fe-MCM-41/O₃ exhibited notably activity with 96.6% IBP removal efficiency within 120 min, while only 78.5% and 80.9% in O₃ alone and Fe-MCM-41/O₃, respectively. Surface Lewis acid sites and metal hydroxyl groups were considered as important factors for O₃ activation and •OH generation. F-Fe-MCM-41 exhibited excellent catalytic performance under acidic and alkaline conditions. Comparative experiments revealed that F doping improved the interfacial reaction, especially the interfacial electron transfer, which resulted in the high catalytic activity of F-Fe-MCM-41. F-Fe-MCM-41 possessed good stability and reusability, with only 5.7% decline for IBP removal in five successive cycles. Furthermore, the possible degradation path of IBP was proposed according to DFT calculation and GC-MS analysis.

Recent Advances in Endocrine Disrupting Compounds Degradation through Metal Oxide-Based Nanomaterials

Endocrine Disrupting Compounds (EDCs) comprise a class of natural or synthetic molecules and groups of substances which are considered as emerging contaminants due to their toxicity and danger for the ecosystems, including human health. Nowadays, the presence of EDCs in water and wastewater has become a global problem, which is challenging the scientific community to address the development and application of effective strategies for their removal from the environment. Particularly, catalytic and photocatalytic degradation processes employing nanostructured materials based on metal oxides, mainly acting through the generation of reactive oxygen species, are widely explored to eradicate EDCs from water. In this review, we report the recent advances described by the major publications in recent years and focused on the degradation processes of several classes of EDCs, such as plastic components and additives, agricultural chemicals, pharmaceuticals, and personal care products, which were realized by using novel metal oxide-based nanomaterials. A variety of doped, hybrid, composite and heterostructured semiconductors were reported, whose performances are influenced by their chemical, structural as well as morphological features. Along with photocatalysis, alternative heterogeneous advanced oxidation processes are in development, and their combination may be a promising way toward industrial scale application.

Occurrence, potential ecological risks, and degradation of endocrine disrupter, nonylphenol, from the aqueous environment

Nonylphenol (NP) is considered a potential endocrine-disrupting chemical affecting humans and the environment. Due to widespread occurrence in the aquatic environment and neuro-, immuno, reproductive, and estrogenic effects, nonylphenol calls for considerable attention from the scientific community, researchers, government officials, and the public. It can persist in the environment, especially soil, for a long duration because of its high hydrophobic nature. Nonylphenol is incorporated into the water matrices via agricultural run-off, wastewater effluents, agricultural sources, and groundwater leakage from the soil. In this regard, assessment of the source, fate, toxic effect, and removal of nonylphenol seems a high-priority concern. Remediation of nonylphenol is possible through physicochemical and microbial methods. Microbial methods are widely used due to ecofriendly in nature. The microbial strains of the genera, Sphingomonas, Sphingobium, Pseudomonas, Pseudoxanthomonas, Thauera, Novosphingonium, Bacillus, Stenotrophomonas, Clostridium, Arthrobacter, Acidovorax, Maricurvus, Rhizobium, Corynebacterium, Rhodococcus, Burkholderia, Acinetobacter, Aspergillus, Pleurotus, Trametes, Clavariopsis, Candida, Phanerochaete, Bjerkandera, Mucor, Fusarium and Metarhizium have been reported for their potential role in the degradation of NP via its metabolic pathway. This study outlines the recent information on the occurrence, origin, and potential ecological and human-related risks of nonylphenol. The current development in the removal of nonylphenol from the environment using different methods is discussed. Despite the significant importance of nonylphenol and its effects on the environment, the number of studies in this area is limited. This review gives an in-depth understanding of NP occurrence, fate, toxicity, and remediation from the environments.

Encapsulation and Release of Doxorubicin from TiO2 Nanotubes: Experiment, Density Functional Theory Calculations, and Molecular Dynamics Simulation

Titanium dioxide (TiO₂) nanotubes are attractive materials for drug-delivery systems because of their biocompatibility, chemical stability, and simple preparation. In this study, we loaded TiO₂ nanotubes with anticancer drug doxorubicin (DOX) experimentally and in all-atom molecular dynamics (MD) simulations. The release of doxorubicin from the nanotubes was studied by high-performance liquid chromatography (HPLC) and confocal Raman spectroscopy, and drug-release profiles were evaluated under various conditions. The polyethylene glycol (PEG) coating and capping of the nanotubes led to a marked increase in the water contact angles from about 16 to 33° in keeping with reduced wettability. The capping retarded the release rate without decreasing the overall release amount. The MD simulations further show that the DOX molecule diffusion coefficients (D_i) are in the order of 10^-10 m²/s. The DOX molecules show a plethora of short- and long-range H-bonding interactions with TiO₂ nanotube walls and water. Calculated radial distribution functions (RDFs) and combined radial/angular distribution functions (CDFs) allowed gauging the strength of these hydrogen bonds. The strength does not fully correlate with the pKa values of DOX atoms which we assign to the confinement of DOX and water in the tubes. The lifetimes of hydrogen bonds between the DOX atoms and water molecules are shorter than that of the DOX^...TiO₂ interactions, and DOX^...DOX aggregation does not play an important role. These results suggest TiO₂ nanotubes as promising candidates for controllable drug-delivery systems for DOX or similar antiproliferative molecules.

SERS-based immunoassay and degradation of CA19-9 mediated by gold nanowires anchored magnetic-semiconductor nanocomposites

Here, straight upward Au nanowires (NWs) were successfully grown onto Fe₃O₄@TiO₂ matrix through a seed-mediated strategy to intensively improve its photocatalysis and SERS performances, facilitating a peculiar recyclable surface-enhanced Raman spectroscopy (SERS)-based immunoassay of CA19-9 in liquid form based on visible light irradiation. Such immunoassay was also supported by a smart heterobifunctional cross-linking agent-mediated probe of anti-CA19-9/4-MBA without metal nanoparticles. A low limit of detection of 5.65 × 10^-4 IUmL^-1 and a wide linear range from 1000 to 0.001 IUmL^-1 were demonstrated through repeated constructing the sandwich immunostructure with only one batch of nanocomposites. Moreover, the actual levels of CA19-9 for colorectal cancer patients were readily measured by the recyclable immunoassay, the results of which are principally consistent with the conventional CLIA detection. Thus, such a green strategy of visible light-induced recyclable immunoassay could be expected to have a potential practicability in the clinical diagnoses of cancer.

Controlled synthesis of mesoporous single-crystalline TiO2 nanoparticles for efficient photocatalytic H2 evolution

Mesoporous single-crystals have emerged as a unique family of functional materials, exhibiting excellent performance in various applications, owing to their well-defined accessible mesoporosity and highly single-crystalline structures. Precise tailoring structures of mesoporous single-crystals at the nanoscale remains an unsolved scientific and technical challenge. Herein, we report a facile and general approach for the synthesis of mesoporous single-crystalline TiO₂ nanoparticles (designated as MSC-TNs) with distinctive traits including tunable morphologies, controllable particle sizes, well dispersity, high hydrophilicity, well-defined mesoporosity and single-crystal nature. Specifically, the amount of water employed in the precursor solution was seen to give fine control over the particle sizes and morphologies of MSC-TNs. MSC-TNs with different sizes show excellent photocatalytic activity in production of hydrogen from water. Under the illumination of 300 W Xe lamp, MSC-TNs were shown to provide good photodegradation performance with Rhodamine 6 G, as well as H₂ production when loaded 1 wt % Pt. In a CH₃OH solution H₂ was evolved with a rate of 8.98 mmol h^-1 g^-1, which is significantly higher than with commercial P25 nanoparticles (4.02 mmol h^-1 g^-1).

In situ growth of well-aligned Ni-MOF nanosheets on nickel foam for enhanced photocatalytic degradation of typical volatile organic compounds

Exploitation of highly efficient catalysts for photocatalytic degradation of volatile organic compounds (VOCs) under visible light irradiation is highly desirable yet challenging. Herein, well-aligned 2D Ni-MOF nanosheet arrays vertically grown on porous nickel foam (Ni-MOF/NF) without lateral stacking were successfully prepared via a facile in situ solvothermal strategy. In this process, Ni foam could serve as both a skeleton to vertically support the Ni-MOF nanosheets and a self-sacrificial template to afford Ni ions for MOF growth. The Ni-MOF/NF nanosheet arrays with highly exposed active sites and light harvesting centres as well as fast mass and e- transport channels exhibited excellent photocatalytic oxidation activity and mineralization efficiency to typical VOCs emitted from the paint spray industry, which was almost impossible for their three-dimensional (3D) bulk Ni-MOF counterparts. A mineralization efficiency of 86.6% could be achieved at 98.1% of ethyl acetate removal. The related degradation mechanism and possible reaction pathways were also attempted based on the electron paramagnetic resonance (EPR) and online Time-of-Flight Mass Spectrometer (PTR-ToF-MS) results.