Degradation Of 4-chlorophenol Research Articles

Proton-coupled electron transfer activation of peroxydisulfate with phosphorylated zero-valent iron

Heterogeneous peroxydisulfate (PDS) activation driven by conventional electron transfer (ET) is often frustrated by low thermodynamic driving force and sluggish kinetics. Herein, we propose a proton-coupled electron transfer (PCET) strategy of PDS activation, by utilizing ball-milled phosphorylated zero-valent iron (P-ZVIbm) as a PCET platform. P-ZVIbm efficiently activated PDS to produce SO4•− and •OH for rapid degradation of 4-chlorophenol in a wide pH range of 3.5–10.5, with rate constants 3–62 times those of the ZVIbm/PDS counterpart. PCET mechanism was evidenced by the pH dependent kinetics, kinetic isotope effect, and proton inventory study. The surface-bound phosphates offer flexible pendant protons (P-O-H) through hydrogen bonds, delocalizing electrons of peroxide O to polarize the O-O bond, thereby facilitating the ET from ZVI for O-O bond cleavage. The work demonstrates the superiority of PCET strategy for heterogeneous PDS activation, and shall guide the design of high-performance Fenton-like catalysts.

Enhanced photocatalytic activity of TiO2 anatase nanoparticles modified with malonic acid under reduced power visible light: Synthesis, characterization and degradation of tetracycline and chlorophenol

Charge transfer complexes (CTCs) between nano-TiO2 and chelating ligands are among the most promising alternatives for photocatalytic applications, such as environmental remediation. However, the development of CTCs based on nano-TiO2 modified with malonic acid (MoA) has not yet been investigated in detail.In this study, TiO2-MoA CTCs, synthesized via sol–gel route, were tested for tetracycline (antibiotic) and chlorophenol (pesticide) photocatalytic degradation with, and without, scavengers of reactive oxidizing species, under low-power visible light (26 W). The TiO2-MoA CTCs were thoroughly characterized. TGA-MS and FTIR analyses revealed malonic acid bonded to the TiO2 surface, while the PL and EPR analyses proved the generation of extrinsic oxygen vacancies due to calcination process of the xerogels.CTCs based on nano-TiO2 strongly bonded to malonic acid, and highly sensitive to visible light, have been synthesized by sol–gel method, followed by calcination at 270 °C in air. The as-prepared CTCs showed very high surface areas (between 180.9 and 323.9 m2.g−1), presence of F+ color centers in the calcined CTCs due to extrinsic oxygen vacancies and high photocatalytic activity, degrading approximately 100 % of the tetracycline after 6 h. In addition, it has been proved that the TiO2-MoA CTCs are efficient sources of •O2– radicals.The findings of this research can be generalized to the synthesis, via sol–gel, of other CTCs between TiO2 and bidentate ligands, such as dicarboxylic acids, and explored for air purification and hydrogen production.

Catalytic dechlorination and deep hydrogenation of 4-chlorophenol in a hydrogen-based internal circulation reactor for efficient wastewater detoxification

Catalytic dechlorination is an attractive technique for chlorophenol degradation but was restricted to the low reaction kinetics and high toxicity of the intermediate products. This work aimed to develop a hydrogen-based internal circulation reactor (H2-ICR) for the efficient detoxification of 4-chlorophenol (4-CP). The structure and catalytic performance of commercial Pt/C, Pd/C, and Ru/C catalysts were systematically investigated. Compared to Pd and Ru, Pt-based catalysts exhibited better performance for the detoxification of chlorophenols. Over 99 % 4-CP was removed within 6 min by employing Pt/C as the catalyst for an initial 4-CP concentration of 2 mM (equivalent to 257 mg L−1). The reaction kinetic constant reaches 0.68 min−1, with the performance almost unchanged at different solution pH (3–11). Mechanistic analysis indicates that phenol hydrogenation is the rate-limiting step on Pt/C. The main product of Pt/C is cyclohexanol, suggesting the simultaneous occurrence of dechlorination and hydrosaturation reactions. In contrast, traditional Pd/C catalysts can hardly catalyze the hydrosaturation reaction, leaving toxic phenol as the main product. Biotoxicity assessment both in silico and by experiment demonstrates that the Pt catalyst can realize efficient detoxification of 4-CP wastewater. Both electron spin resonance (ESR) and radical quenching experiments confirmed the pivotal role of atomic hydrogen (H*). This study provides useful guidance for the design of hydrogenation catalysts and reactors with high safety, which may lead to a paradigm shift for chlorophenol wastewater remediation.

Hydrothermally Synthesized Z-Scheme Nanocomposite of ZIF-9 Modified MXene for Photocatalytic Degradation of 4-Chlorophenol.

4-Chlorophenol (4CP) is a well-known environmental contaminant often detected in wastewater, generally arising from industrial processes such as chemical manufacture, pharmaceutical production, and pesticide formulation. 4CP is a matter of great concern since it is persistent and has the potential to have harmful impacts on both aquatic ecosystems and human health, owing to its hazardous and mutagenic properties. Hence, degradation of 4CP is of utmost significance. This research investigates the photocatalytic degradation of 4CP using a novel Z-scheme heterojunction nanocomposite composed of MXene and ZIF-9. The nanocomposite is synthesized through a two-step hydrothermal method and thoroughly characterized by using XRD, SEM, UV-visible spectroscopy, zeta potential, and electrochemical impedance spectroscopy studies, confirming successful fabrication with improved surface properties. The comparative photocatalytic degradation studies between pristine materials and the nanocomposite were performed, and significant enhancement in performance was observed. The effect of pH on the degradation efficiency is also explored and correlated with the surface charge. The Z-scheme photocatalysis mechanism is proposed, which is supported by time-resolved photoluminescence studies and scavenger experiments. The reusability of the nanocomposite is also evaluated. The study contributes to the development of efficient and sustainable photocatalysts for wastewater treatment.

Synergistic degradation of formaldehyde and chlorophenols in N-CQDs/BiOBr photocathode-coupled microbial fuel cells and the enhancement of power production efficiency

p-Chlorophenol (4-CP) is a recalcitrant pollutant with high toxicity that bioaccumulates and persists in the environment. In order to remove most of 4-CP in a short time, this study constructed an N-CQDs/BiOBr photocatalytic cathode microbial fuel cell (PMFCs) system, introduced formaldehyde wastewater into the biological anode, and enhanced the electronic interaction between the cathode and anode, thus realizing the high efficiency of the degradation of 4-CP and the production of electric energy. The results showed that the removal rate of 4-CP (30 mg/L) by PMFCs was 86.8%, which was higher than that of MFC (65%) and photocatalysis (11.73%) combined, showing a good synergistic effect. In addition, driven by the continuous negative bias provided by the anode, the electrons generated at the anode preferentially combine with the photogenerated holes at the cathode, which increases the power generation of the PMFCs, and achieves a maximum power density of 286.225 W/ m2 and a maximum open-circuit voltage of 0.518 V. The electrochemical properties of PMFCs were characterized by cyclic voltammetry and electrochemical impedance spectroscopy, and the results showed that the charge transfer resistance of PMFCs was only half that of MFC. Free radical trapping experiments have confirmed that ∙O2- is the main reactive oxidizing substance. Subsequently, a possible electron transport mechanism was proposed, and five degradation pathways of 4-CP were identified using liquid chromatography-mass spectrometry. In conclusion, this technology is a good alternative method to improve the treatment efficiency of refractory wastewater in practical applications.

Enhanced oxidation of organic pollutants by regulating the interior reaction region of reactive electrochemical membranes

Reactive electrochemical membrane (REM) emerges as an attractive strategy for the elimination of refractory organic pollutants that exist in wastewater. However, the limited reaction sites in traditional REMs greatly hinder its practical application. Herein, a feed-through coating methodology was developed to realize the uniform loading of SnO2-Sb catalysts on the interior surface of a REM. The uniformly coated REM (Unif-REM) exhibited 2.4 times higher reaction kinetics (0.29 min–1) than that of surface coated REM (Surf-REM) for the degradation of 2 mM 4-chlorophenol (4-CP), rendering an energy consumption as low as 0.016 kWh gTOC–1. The fast degradation of various emerging contaminants, e.g., sulfamethoxazole (SMX), ofloxacin (OFLX), and tetracycline (TC), also confirms its superior oxidation capability. Besides, the Unif-REM exhibited good performance in generating hydroxyl radicals (•OH) and a relatively long service lifetime. The simulation of spatial current distribution demonstrates that the interior reaction region in the Unif-REM channels can be drastically extended, thereby maximizing the surface coupling of mass diffusion and electron transfer. This study offers an in-depth look at the spatially confined reactions in REM and provides a reference for the design of electrochemical systems with economically efficient water purification.

Fenton-like system of UV/Glucose-oxidase@Kaolin coupled with organic green rust: UV-enhanced enzyme activity and the mechanism of UV synergistic degradation of photosensitive pollutants

This study introduces the UV/glucose-oxidase@Kaolin (GOD@Kaolin) coupled organic green rust (OGR) system (UV/OGR/GOD@Kaolin) to investigate the promotion of glucose oxidase activity by UV light and its synergistic degradation mechanism for photosensitive pollutants, specifically targeting the efficient degradation of 4-chlorophenol (4-CP). The enzyme system demonstrates its ability to overcome drawbacks associated with traditional Fenton systems, including a narrow pH range and high localized concentration of H2O2, by gradually releasing hydrogen peroxide in situ within a neutral environment. In the presence of UV radiation under specific conditions, enhanced enzyme activity is observed, resulting in increased efficiency in pollutant removal. The gradual release of hydrogen peroxide plays a crucial role in preventing unwanted reactions among active substances. These unique features facilitate the generation of highly reactive species, such as Fe(IV)O, •OH, and •O2−, tailored to efficiently target the organic components of interest. Additionally, the system establishes a positive iron cycle, ensuring a sustained reactive capability throughout the degradation process. The results highlight the UV/OGR/GOD@Kaolin system as an effective and environmentally friendly approach for the degradation of 4-CP, and the resilience of the enzyme extends the system's applicability to a broader range of scenarios.

Degradation of 4-chlorophenol through in situ generation of reactive chlorine species in a Zn2CoOx electrocatalytic system

Chloride ion significantly impacts the degradation efficiency of organic pollutants in chemical industrial wastewater during electrocatalytic process, therefore utilization of Cl− to in situ produce reactive chlorine species (RCS) is desired for electrocatalytic degradation of pollutants. We developed a novel catalyst by incorporating Zn into CoOx (ZnnCoOx) as anode for the electrocatalytic removal of 4-chlorophenols (4-cp) in Cl−-containing wastewater. Characterization and electrochemical performance of ZnnCoOx catalysts indicated that Zn incorporation increased Co2+/Co3+ ratio, resulting in lattice distortion and the formation of oxygen vacancy (OV). Electrocatalytic experiments showed that Zn2CoOx (i.e., ZnCo = 2:1) had the highest electrochemical reactivity, and the 4-cp degradation rates (kobs) showed a positive correlation with OV. The identified reactive species involved in 4-cp degradation included O2•− and RCS. The formation mechanism of reactive species and the degradation pathways of 4-cp during electrocatalytic process using the Zn2CoOx anode were proposed. Overall, the developed ZnnCoOx catalyst as anode can utilize Cl− to in situ produce RCS and exhibit an effective performance on the 4-cp degradation in Cl−-containing wastewater.

Synergistic potency of ultrasound and solar energy towards oxidation of 2,4-dichlorophenol: a chemometrics approach.

Industrial units based on chemical processes-the textile and paper industries-are major sources of chlorophenols in the environment, and chlorophenolic compounds persist within the environment for a long time with high toxicity levels. The photo-assisted Fenton's and photocatalysis processes were investigated for the degradation of chlorophenols in the present study. Response surface methodology was employed to get optimised conditions for photocatalysis and photo-Fenton process-governing factors, thus, yielding a profound removal efficiency. Under optimised conditions, with a photocatalyst dose of 0.2 g/L, oxidant concentration of 10.0 mM and pH 5.0, complete removal of 2,4-dichlorophenol (2,4-DCP) was observed in 210 minutes in photocatalytic treatment. In the case of the photo-Fenton process, at an H2O2 dose of 5.0 mM and Fe2+ concentration of 0.5 mM, the organic pollutant was eliminated within 5 minutes of reaction time under acidic conditions (pH 3.0). The RSM model reported the perfect fit of experimental data with the predicted response. Among different isotherm models, the Langmuir isotherm was the best fit. The process followed pseudo-first order rate kinetics among various kinetics models. For the obtained optimised conditions, sonication and solar energy-driven processes were incorporated to study enhanced mineralisation. The solar-assisted Fenton process reported maximum mineralisation (90%) and cost-effective ($0.01/litre for 100 mg/L 2,4-DCP) treatment among different hybrid oxidation processes. The work provides insight into harnessing the naturally available solar energy, reducing the overall treatment cost and opting for a sustainable treatment method.

Degradation and metagenomic analysis of 4-chlorophenol utilizing multiple metal tolerant bacterial consortium.

Chlorophenols are persistent environmental pollutants used in synthesizing dyes, drugs, pesticides, and other industrial products. The chlorophenols released from these processes seriously threaten the environment and human health. The present study describes 4-chlorophenol (4-CP) degradation activity and metagenome structure of a bacterial consortium enriched in a 4-CP-containing medium. The consortium utilized 4-CP as a single carbon source at a wide pH range, temperature, and in the presence of heavy metals. The immobilized consortium retained its degradation capacity for an extended period. The 4-aminoantipyrine colorimetric analysis revealed complete mineralization of 4-CP up to 200mg/L concentration and followed the zero-order kinetics. The addition of glycerol and yeast extract enhanced the degradation efficiency. The consortium showed both ortho- and meta-cleavage activity of catechol dioxygenase. Whole genome sequence (WGS) analysis revealed the microbial compositions and functional genes related to xenobiotic degradation pathways. The identified genes were mapped on the KEGG database to construct the 4-CP degradation pathway. The results exhibited the high potential of the consortium for bioremediation of 4-CP contaminated sites. To our knowledge, this is the first report on WGS analysis of a 4-CP degrading bacterial consortium.

A photocatalyst with an enhanced Schottky effect and an efficient electron-transfer channel fabricated by assembling Ni–WC heterojunction nanoparticles on g-C3N4 for highly efficient removal of chlorophenols

An enhanced Schottky effect and efficient electron-transfer channel in Ni–WC/CN enable the efficient separation and transfer of photoexcited electrons, which boosts efficient photocatalytic degradation of toxic 4-chlorophenol.

Green synthesis of N-doped ZnS@Zeolite nanocomposite for the effective degradation of Rose Bengal dye and 4-chlorophenol

Green synthesis of N-doped ZnS@Zeolite nanocomposite for the effective degradation of Rose Bengal dye and 4-chlorophenol

Optimized preparation of nitrogen-modified ceria for stable and efficient degradation of 2,4-DCP

Chlorophenols have been frequently detected in the environment, posing potential threats to both the natural ecosystem and human health. Semiconductor photocatalytic degradation of chlorophenols has become a prominent research focus. However, the development of high-performance and stable photocatalysts remains challenging. In this work, the nitrogen-modified ceria (N-CeO2) was optimally prepared by microwave-assisted method and utilized for photocatalytic degradation of 2,4-DCP. The CeO2 photocatalyst with 10% nitrogen doping (10% N-CeO2) prepared under the optimal condition (microwave power of 560 W for 2 min and calcination temperature of 400 °C for 2 h) degraded 2,4-DCP with the highest removal efficiency of 93.51%. It was identified that the optimally prepared 10% N-CeO2 photocatalyst had the nanometer size with surface imperfections and increased BET surface, and showed strongest photocurrent response and lowest charge transfer resistance among all the prepared materials. Additionally, an analysis of the band gap structure revealed that the band gap of 10% N-CeO2 decreased from 3.05 eV (for pure CeO2) to 2.42 eV, resulting in enhanced light absorption capacity. The radical trapping experiments and electron paramagnetic resonance (EPR) proved that the active species contributed to the degradation of 2,4-DCP mainly as •OH, •O2-. The potential photocatalytic degradation mechanism of 2,4-DCP was a continuous dechlorination and hydroxylation process with complete mineralization of the pollutant to CO2 and H2O. This work can provide a feasible way to prepare high-efficiency nitrogen-doped ceria photocatalysts with great potential for the removal of chlorophenols.

Exploring 2,4,6-Trichlorophenol Degradation Characteristics and Functional Metabolic Gene Abundance Using Sludge Fermentation Broth as the Carbon Source

The use of sludge fermentation broth (FB) as a co-metabolic carbon source for treating 2,4,6-trichlorophenol (2,4,6-TCP) wastewater is a novel strategy. The key to the feasibility of this strategy is whether the FB can promote the growth of functional microorganisms that are capable of degrading 2,4,6-TCP. This study focused on long-term acclimatized sludge and investigated the impact of key operating parameters such as the sludge FB concentration and the influent concentration of 2,4,6-TCP on the removal efficiency of chlorophenol. The research findings revealed that when the influent concentration of sludge FB exceeded 300 mg COD/L, it significantly inhibited the degradation of 2,4,6-TCP. Simulation experiments using individual VFA components as influent carbon sources showed that excessive propionic acid addition can inhibit the degradation of 2,4,6-TCP, indicating the need to control the concentration of propionic acid in the fermentation conditions. Metagenomic analysis further showed that sludge FB can promote the enrichment of microbial chlorophenol degradation genes, including PcpA, pcaF, pcaI, Mal-r, chqB, and fadA. The abundances of these six chlorophenol degradation genes were as follows: 1152 hits (PcpA), 112 hits (pcaF), 10,144 hits (pcaI), 12,552 hits (Mal-r), 8022 hits (chqB), and 20,122 hits (fadA). Compared with other types of carbon sources, sludge FB demonstrates distinct advantages in terms of leading to the highest chlorophenol degradation concentration and the abundance of functional microbial communities. This study has successfully demonstrated the feasibility of using sludge FB as a co-metabolic carbon source for the degradation of 2,4,6-TCP.

Parametric Mathematical Model of the Electrochemical Degradation of 2-Chlorophenol in a Flow-by Reactor under Batch Recirculation Mode

2-Chlorophenol (2-CP) is a dangerous organic contaminant found in wastewater. In this work, 2.5 L of a 2-CP solution (1 mol/m3) was electrochemically treated in a flow-by reactor equipped with two boron-doped diamond electrodes (BDD) under batch recirculation mode for a period for 4 h, a current density of 0.14 A/cm2, a volumetric flow rate of 1 L/min, and pH = 7.3. In this work, a parametric mathematical model of the degradation efficiency of 2-CP was developed using an axial dispersion model and a continuous stirred tank for the flow-by reactor (FBR), which was constructed using a shell mass balance considering the dispersion and convection terms and the reservoir tank (CST), which was constructed using a mass balance of 2-CP. The parametric mathematic model of the electrochemical degradation of 2-chlorophenol was numerically resolved by employing the software package COMSOL Multiphysics® V. 5.3, where a mass transfer equation for diluted species and a global differential equation represents the FBR and CST, respectively. The results indicate that the parametric mathematical model proposed in this research fits the experimental results, and this is supported by the index performance values such as the determination coefficient (R2 = 0.9831), the mean square error (MSE = 0.0307), and the reduced root-mean-square error (RMSE = 0.1754). Moreover, the degradation efficiency of 2-CP estimated by the proposed model achieves 99.06%, whereas the experimental degradation efficiency reached 99.99%, a comparative error of 0.93%. This corroborates the predictive ability of the developed mathematical model and the effectiveness of the employed electrooxidation process. Finally, a 0.143 USD/L total operating cost for the electrochemical plant was estimated.

Metal-free catalysts with local fluorination regulation for peroxymonosulfate activation: Nearly 100 % singlet oxygen production for selective degradation of aqueous organic pollutants

Generating singlet oxygen (1O2) via activating peroxymonosulfate (PMS) is crucial for the selective removal of organic pollutants in aquatic environments. However, achieving efficient and selective conversion of PMS into 1O2 without consuming energy or metals remains a significant challenge. In this study, graphite phase carbon nitride (g-C3N4) was locally fluorinated via a simple polymerization method. The local fluorinated g-C3N4 (FCN) was used as a metal-free catalyst to activate PMS, enabling highly efficient degradation of 4-chlorophenol (100 %) and detoxification. The FCN/PMS system demonstrates exceptional selectivity for electron-rich pollutants, functions effectively across a broad pH range (2–10), and exhibits remarkable interference resistances to background scavenging ions and natural organic compounds. Furthermore, quenching experiments, probe tests, electron paramagnetic spin resonance measurements, electrochemical characterizations, and theoretical calculations demonstrated that 1O2 was the only reactive species in the catalytic process. Local fluorination regulated the electronic structure of g-C3N4, juxtaposing electron-rich fluorine with electron-deficient carbon dual active sites. This modification alters the electron transfer direction between PMS and g-C3N4, allowing for nearly 100 % selective generation of 1O2via dual electron transfer channels without the need for energy or metals. This study provides a new strategy for designing metal-free heterogeneous catalysts to selectively generate 1O2 in a green way and can facilitate the wider applications of advanced oxidation processes for water purification.

Visible-Light-Active BiOI/TiO2 Heterojunction Photocatalysts for Remediation of Crude Oil-Contaminated Water.

In this study, BiOI-sensitized TiO2 (BiOI/TiO2) nanocomposites with different levels of BiOI deposited via sequential ionic layer adsorption and reaction (SILAR) have been explored for the degradation of methyl orange, 4-chlorophenol (4-CP), and crude oil in water under visible (>400 nm) irradiation with excellent degradation performance. The reaction progress for methyl orange and 4-chlorophenol was monitored by a UV-vis spectrophotometer, and the degradation of the crude oil hydrocarbons was determined by GC-MS. The BiOI/TiO2 heterojunction improves separation of photogenerated charges, which enhances the degradation efficiency. Evaluation of the visible-light photocatalytic performance of the synthesized catalysts against methyl orange degradation confirmed that four SILAR cycles are the optimal deposition condition for the best degradation efficiency. The efficiency was further confirmed by degrading 4-CP and crude oil, achieving 38.30 and 85.62% degradation, respectively, compared with 0.0% (4-CP) and 70.56% (crude oil) achieved by TiO2. The efficiency of TiO2 in degrading crude oil was mainly due to adsorption along with photolysis. This study provides a simple and cost-effective alternative to traditional remediation methods requiring high energy consumption for remediation of crude oil-polluted water and refinery wastewater using visible-light photocatalysis along with adsorption.

Adaptive laboratory evolution of Rhodococcus rhodochrous DSM6263 for chlorophenol degradation under hypersaline condition

BackgroundNormally, a salt amount greater than 3.5% (w/v) is defined as hypersaline. Large amounts of hypersaline wastewater containing organic pollutants need to be treated before it can be discharged into the environment. The most critical aspect of the biological treatment of saline wastewater is the inhibitory/toxic effect exerted on bacterial metabolism by high salt concentrations. Although efforts have been dedicated to improving the performance through the use of salt-tolerant or halophilic bacteria, the diversities of the strains and the range of substrate spectrum remain limited, especially in chlorophenol wastewater treatment.ResultsIn this study, a salt-tolerant chlorophenol-degrading strain was generated from Rhodococcus rhodochrous DSM6263, an original aniline degrader, by adaptive laboratory evolution. The evolved strain R. rhodochrous CP-8 could tolerant 8% NaCl with 4-chlorophenol degradation capacity. The synonymous mutation in phosphodiesterase of strain CP-8 may retard the hydrolysis of cyclic adenosine monophosphate (cAMP), which is a key factor reported in the osmoregulation. The experimentally verified up-regulation of intracellular cAMP level in the evolved strain CP-8 contributes to the improvement of growth phenotype under high osmotic condition. Additionally, a point mutant of the catechol 1,2-dioxygenase, CatAN211S, was revealed to show the 1.9-fold increment on activity, which the mechanism was well explained by molecular docking analysis.ConclusionsThis study developed one chlorophenol-degrading strain with extraordinary capacity of salt tolerance, which showed great application potential in hypersaline chlorophenol wastewater treatment. The synonymous mutation in phosphodiesterase resulted in the change of intracellular cAMP concentration and then increase the osmotic tolerance in the evolved strain. The catechol 1,2-dioxygenase mutant with improved activity also facilitated chlorophenol removal since it is the key enzyme in the degradation pathway.

The inhibitory mechanism of humic acids on photocatalytic generation of reactive oxygen species by TiO2 depends on the crystalline phase

To enable the practical use of TiO2 for photocatalytic water treatment, it is important to understand how dissolved natural organic matter affects its photocatalytic activity and the mechanisms involved in generating reactive oxygen species (ROS). In this study, we systematically investigated the inhibitory effects of humic acids (HA) on 4-chlorophenol (4-CP) degradation using two common TiO2 crystalline phases (anatase and rutile) individually. HA strongly hindered the photocatalytic activity of anatase, with an Ra (the ratio of the first-order rate constant for 4-CP degradation in the absence vs. presence of 30 mg/L HA) of 2.30 (±0.13). This ratio was significantly higher than that of rutile (Rr = 1.21 ± 0.08), which was less susceptible to this inhibitory effect and even exhibited improved photocatalytic activity at HA concentrations below 20 mg/L. Similar trends were observed for various HA sources, corroborating the crystalline-phase-dependent effect of HA. Adsorption experiments, Fourier transform infrared spectroscopy, and photoelectrochemical analyses suggested that the adsorption mechanisms and hole-scavenging effect of HA on the two TiO2 polymorphs did not differ. Importantly, scavenger, probe, and electron spin resonance experiments revealed that the difference in inhibitory effects of HA originate from the distinct ROS generation mechanisms for the two polymorphs. The oxygen reduction pathway for OH generation over anatase was hindered by surface-adsorbed HA, while the water oxidation pathway for OH generation over rutile was less affected. Furthermore, surface-adsorbed HA boosted O2− generation on rutile, increasing 4-CP degradation efficiency. This mechanistic insight into NOM-TiO2 interactions informs materials selection and strategies for higher TiO2 photocatalytic performance in different water matrices.

Photoinactivation of microorganisms and photodegradation of pollutants using phthalocyanines supported on nanofibers and glass wool

Neutral and cationic zinc and indium phthalocyanines (Pcs) are anchored onto polyacrylonitrile nanofibers (NFs) and glass wools (GWs). The properties of these composites were evaluated and compared. Thermal gravimetric analysis showed that GWs had higher stability than NFs. The nanofibers had a higher loading of > 50 % compared to < 35 % for glass wools. The singlet oxygen quantum yield was proportional to the loading. The degradation of 4-chlorophenol, methyl orange, and methylene blue, and the antimicrobial activity (photodynamic antimicrobial chemotherapy) of the composites were evaluated. It was revealed that the NFs showed a combination of photocatalytic and adsorption properties against methylene blue. The NFs degraded the organic pollutants faster than GWs. The cationic composites showed higher antimicrobial activities than their neutral derivates. The results show a promising application window of the cationic Pc-nanofibers.