A hybridization approach to efficient TiO2 photodegradation of aqueous benzalkonium chloride

Photochemical fate of quaternary ammonium compounds (QACs) and degradation pathways predication through computational analysis

Quaternary ammonium compounds (QACs) are commonly used in many products, such as disinfectants, detergents and personal care products. However, their widespread use has led to their ubiquitous presence in the environment, posing a potential risk to human and environmental health. Several methods, including direct and indirect photodegradation, have been explored to remove QACs such as benzylalkyldimethyl ammonium compounds (BACs) and alkyltrimethyl ammonium compounds (ATMACs) from the environment. Hence, in this research, a systematic review of the literature was conducted using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) method to understand the fate of these QACs during direct and indirect photodegradation in UV/H2O2, UV/PS, UV/PS/Cu2+, UV/chlorine, VUV/UV/chlorine, O3/UV and UV/O3/TiO2 systems which produce highly reactive radicals that rapidly react with the QACs, leading to their degradation. As a result of photodegradation, several transformation products (TPs) of QACs are formed, which can pose a greater risk to the environment and human health than the parent QACs. Only limited research in this area has been conducted with fewer QACs. Hence, quantum mechanical calculations such as density functional theory (DFT)-based computational calculations using Gaussian09 software package were used here to explain better the photo-resistant nature of a specific type of QACs, such as BACs C12-18 and ATMACs C12, C14, C18, and their transformation pathways, providing insights into active sites participating in the phototransformation. Recognizing that different advanced oxidation processes (AOPs) come with pros and cons in the elimination of QACs, this review also highlighted the importance of implementing each AOP concerning the formation of toxic transformation products and electrical energy per order (EEO), especially when QACs coexist with other emerging contaminants (ECs).

Adsorption and photocatalytic removal of Ibuprofen by activated carbon impregnated with TiO2 by UV-Vis monitoring

The removal of Ibuprofen was investigated by activated carbon impregnated with TiO₂. Emphasis was given on the effect of different parameters, such as composite type, initial Ibuprofen concentration (5-25 mg/L), temperature (22-28 °C) and pH (acidic and alkaline solution). The experiment was carried out in a self-made tubular flow reactor, with one 15 W monochromatic UV lamp (254 nm). The composite AC90T10 gives the highest removal degree of 92% of Ibuprofen solution under UV light within 4 h, due to synergy of adsorption and photodegradation. It was found that weight ratio of composite/Ibuprofen has limited effect on the removal degree within the concentration range (5-25 mg/L), but reaction time under UV light (4 h) and pH (acidic solution) are very important. The kinetic experimental data obtained at pH 4.3 at 25 °C on different composites were fitted to pseudo-first, pseudo-second and Elovich models, obtaining a high accuracy based on R² values. From the results, composites of granular activated carbon and TiO₂ can enhance removal of Ibuprofen effectively, making recycle process much easier and less costly, which can be a promising method in future water treatment.

Characterization of the chemicals used in hydraulic fracturing fluids for wells located in the Marcellus Shale Play

Hydraulic fracturing, coupled with the advances in horizontal drilling, has been used for recovering oil and natural gas from shale formations and has aided in increasing the production of these energy resources. The large volumes of hydraulic fracturing fluids used in this technology contain chemical additives, which may be toxic organics or produce toxic degradation byproducts. This paper investigated the chemicals introduced into the hydraulic fracturing fluids for completed wells located in Pennsylvania and West Virginia from data provided by the well operators. The results showed a total of 5071 wells, with average water volumes of 5,383,743 ± 2,789,077 gal (mean ± standard deviation). A total of 517 chemicals was introduced into the formulated hydraulic fracturing fluids. Of the 517 chemicals listed by the operators, 96 were inorganic compounds, 358 chemicals were organic species, and the remaining 63 cannot be identified. Many toxic organics were used in the hydraulic fracturing fluids. Some of them are carcinogenic, including formaldehyde, naphthalene, and acrylamide. The degradation of alkylphenol ethoxylates would produce more toxic, persistent, and estrogenic intermediates. Acrylamide monomer as a primary degradation intermediate of polyacrylamides is carcinogenic. Most of the chemicals appearing in the hydraulic fracturing fluids can be removed when adopting the appropriate treatments.

Advances in Subcritical Hydro-/Solvothermal Processing of Graphene Materials

Many promising graphene-based materials are kept away from mainstream applications due to problems of scalability and environmental concerns in their processing. Hydro-/solvothermal techniques overwhelmingly satisfy both the aforementioned criteria, and have matured as alternatives to wet-chemical methods with advances made over the past few decades. The insolubility of graphene in many solvents poses considerable difficulties in their processing. In this context hydro-/solvothermal techniques present an ideal opportunity for processing of graphenic materials with their versatility in manipulating the physical and thermodynamic properties of the solvent. The flexibility in hydro-/solvothermal techniques for manipulation of solvent composition, temperature and pressure provides numerous handles to manipulate graphene-based materials during synthesis. This review provides a comprehensive look at the subcritical hydro-/solvothermal synthesis of graphene-based functional materials and their applications. Several key synthetic strategies governing the morphology and properties of the products such as temperature, pressure, and solvent effects are elaborated. Advances in the synthesis, doping, and functionalization of graphene in hydro-/solvothermal media are highlighted together with our perspectives in the field.

UV/chlorine as an advanced oxidation process for the degradation of benzalkonium chloride: Synergistic effect, transformation products and toxicity evaluation

Benzalkonium chlorides (BACs), as typical cationic surfactants and biocides widely applied in household and industrial products, have been frequently detected as micropollutants in many aquatic environments. In this study, the combination of UV irradiation and chlorine (UV/chlorine), a newly interested advanced oxidation process, was used to degrade dodecylbenzyldimethylammonium chloride (DDBAC). UV/chlorine showed synergistic effects on DDBAC degradation comparing to UV irradiation or chlorination alone. Radical quenching experiments indicated that degradation of DDBAC by UV/chlorine involved both UV photolysis and radical species oxidation, which accounted for 48.4% and 51.6%, respectively. Chlorine dosage and pH are essential parameters affecting the treatment efficiency of UV/chlorine. The pseudo first order rate constant (k_{obs, DDBAC}) increased from 0.046 min^-1 to 0.123 min^-1 in response to chlorine dosage at 0-150 mg/L, and the degradation percentage of DDBAC within 12 min decreased from 81.4% to 56.6% at pH 3.6-9.5. Five main intermediates were identified and semi-quantified using HPLC-MS/MS and a possible degradation pathway was proposed. The degradation mechanisms of DDBAC by UV/chlorine included cleavage of the benzyl-nitrogen bond and hydrogen abstraction of the alkyl chain. Trichloromethane (TCM), chloral hydrate (CH), trichloropropanone (TCP), dichloropropanone (DCP) and dichloroacetonitrile (DCAN) were detected using GC-ECD. The formation of chlorinated products increased rapidly initially, then decreased (TCM, TCP, DCP and DCAN) or remained stable (CH) with extended treatment. The actual formation of TCM peaked at 30 min (50.3 μg/L), while other chlorinated products did not exceed 10 μg/L throughout the process. Based on the luminescent bacterial assay, DDBAC solution underwent almost complete detoxification subjected to UV/chlorine treatment for 120 min, which is more effective than UV irradiation or chlorination alone.

Mechanism and toxicity research of benzalkonium chloride oxidation in aqueous solution by H2O2/Fe(2+) process

As widely used disinfectants, the pollution caused by benzalkonium chloride (BAC) has attracted a lot of attention in recent years. Since it is not suitable for biodegradation, BAC was degraded firstly by Fenton advanced oxidation technologies (AOTs) in this research to enhance the biodegradability of the pollutions. The result revealed that the optimal molar ratio of H2O2/Fe(2+) for BAC degradation was 10:1, and the COD removal rate was 32 %. To clarify the pathway of degradation, the technique of GC-MS was implemented herein to identify intermediates and the toxicity of those BAC intermediates were also novelty tested through microbial fuel cells (MFC). The findings indicated that ten transformation products including benzyl dimethyl amine and dodecane were formed during the H2O2/Fe(2+) processes, which means the degradation pathway of BAC was initiated both on the hydrophobic (alkyl chain) and hydrophilic (benzyl and ammonium moiety) region of the surfactant. The toxicity of BAC before and after treated by Fenton process was monitored through MFC system. The electricity generation was improved 337 % after BAC was treated by H2O2/Fe(2+) oxidation processes which indicated that the toxicity of those intermediates were much lower than BAC. The mechanism and toxicity research in this paper could provide the in-depth understanding to the pathway of BAC degradation and proved the possibility of AOTs for the pretreatment of a biodegradation process.