Photocatalytic degradation of industrial pulp and paper mill effluent using synthesized magnetic Fe2O3-TiO2: Treatment efficiency and characterizations of reused photocatalyst

Selective removal of sulfamethoxazole by a novel double Z-scheme photocatalyst: Preferential recognition and degradation mechanism

Sulfamethoxazole (SMX) is a significant environmental concern due to its adverse effects and ecological risks. SMX elimination in aquatic environments via photocatalysis presents a viable solution, given its high oxidation potential. However, such a solution remains controversial, primarily due to a lack of selectivity. Here we introduce a molecularly imprinted TiO2@Fe2O3@g-C3N4 (MFTC) photocatalyst designed for the selective degradation of SMX. To assess MFTC's selectivity, we applied it to degrade synthetic wastewater containing SMX alongside interfering species sulfadiazine (SDZ), ibuprofen (IBU), and bisphenol A (BPA). The results demonstrated a selective degradation efficiency rate of 96.8%, nearly twice that of competing pollutants. The molecularly imprinted sites within the catalyst played a crucial role by selectively capturing SMX and enhancing its adsorption, thereby improving catalytic efficiency. The degradation process involved •OH and •O2- free radicals, with a newly proposed double Z-scheme mechanism and potential pathway for SMX degradation by the MFTC photocatalytic system. This study enriches the application of photocatalysis using molecularly imprinted nanocomposite materials for treating complex pollutant mixtures in water.

A critical review on environmental risk and toxic hazards of refractory pollutants discharged in chlorolignin waste of pulp and paper mills and their remediation approaches for environmental safety

Agro-based pulp and paper mills (PPMs) inevitably produce numerous refractory pollutants in their wastewater, including chlorolignin, chlorophenols, chlorocatechols, chloroguaiacol, cyanide, furan, dioxins, and other organic compounds, as well as various heavy metals, such as nickel (Ni), zinc (Zn), chromium (Cr), iron (Fe), lead (Pb), arsenic (As), etc. These pollutants pose significant threats to aquatic and terrestrial life due to their cytogenotoxicity, mutagenicity, impact on sexual organs, hormonal interference, endocrine disruption, and allergenic response. Consequently, it is crucial to reclaim pulp paper mill wastewater (PPMW) with high loads of refractory pollutants through effective and environmentally sustainable practices to minimize the presence of these chemicals and ensure environmental safety. However, there is currently no comprehensive published review providing up-to-date knowledge on the fate of refractory pollutants from PPMW in soil and aquatic environments, along with valuable insights into the associated health hazards and remediation methods. This critical review aims to shed light on the potential adverse effects of refractory pollutants from PPMW on natural ecosystems and living organisms. It explores existing effective treatment technologies for remediating these pollutants from wastewater, highlighting the advantages and disadvantages of each approach, all in pursuit of environmental safety. Special emphasis is placed on emerging technologies used to decontaminate wastewater discharged from PPMs, ensuring the preservation of the environment. Additionally, this review addresses the major challenges and proposes future research directions for the proper disposal of PPMW. It serves as a comprehensive source of knowledge on the environmental toxicity and risks associated with refractory pollutants in PPMW, making it a valuable reference for policymakers and researchers when selecting appropriate technologies for remediation. The scientific community, concerned with mitigating the widespread risks posed by refractory pollutants from PPMs, is expected to take a keen interest in this review.

3D N-doped carbon derived from zeolitic imidazole framework as heterogeneous catalysts for decomposition of pulp and paper mill effluent: Optimization and kinetics study

Three specific catalysts, namely ZIF-67 (zeolitic imidazolate framework-67), Co@NCF (Co@Nitrogen-Doped Carbon Framework), and 3D NCF (Three-Dimensional Nitrogen-Doped Carbon Framework), were prepared and studied for pulp and paper mill effluent degradation using heterogeneous activation of peroxymonosulfate (PMS). Numerous characterizations, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and N2 adsorption, were used to characterize the properties of three different catalysts. 3D NCF is remarkably effective at heterogeneous activation of PMS to generate sulfate radicals to degrade pulp and paper mill effluent (PPME) compared to the other as-prepared catalysts. The catalytic activity reveals a sequence of 3D NCF > Co@NCF > ZIF-67.3D NCF could degrade organic pollutants in 30 min at an initial COD concentration of 1146 mg/L of PPME, 0.2 g/L catalysts, 2 g/L PMS, and 50 °C. Consequently, it was observed that the degradation of PPME using 3D NCF followed first-order kinetics, with an activation energy of 40.54 kJ mol-1. Overall, 3D NCF/PMS system reveals promising performance for PPME removal.

Comparison of photocatalysis and photolysis of 2,2,4,4-tetrabromodiphenyl ether (BDE-47): Operational parameters, kinetic studies, and data validation using three modern machine learning models

Polybrominated diphenyl ethers (PBDEs) are halogenated organic compounds that are among the major pollutants of water, and there is an urgent need for their removal. This work compared the application of two techniques, i.e., photocatalytic reaction (PCR) and photolysis (PL), for 2,2,4,4- tetrabromodiphenyl ether (BDE-47) degradation. Although a limited degradation of BDE-47 was observed by photolysis (LED/N₂), photocatalytic oxidation by using TiO₂/LED/N₂ proved to be effective in the degradation of BDE-47. The use of a photocatalyst enhanced the extent of BDE-47 degradation by around 10% at optimum conditions in anaerobic systems. Experimental results were systematically validated through modeling with three new and powerful Machine Learning (ML) approaches, including Gradient Boosted Decision Tree (GBDT), Artificial Neural Network (ANN), and Symbolic Regression (SBR). Four statistical criteria (Coefficient of Determination (R²), Root Mean Square Error (RMSE), Average Relative Error (ARER), and Absolute Error (ABER)) were calculated for model validation. Among the applied models, the developed GBDT was the desirable model for predicting the remaining concentration (Ce) of BDE-47 for both processes. Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD) results confirmed that BDE-47 mineralization required additional time than its degradation in both PCR and PL systems. The kinetic study demonstrated that BDE-47 degradation for both processes followed the pseudo-first-order form of the Langmuir-Hinshelwood (L-H) model. More importantly, the calculated electrical energy consumption of photolysis was shown to be ten percent higher than that for photocatalysis, possibly due to the higher irradiation time required in direct photolysis, which in turn increases electricity consumption. This study is useful in proposing a feasible and promising treatment process for the degradation of BDE-47.

Photo-Fenton assisted AgCl and P-doped g-C3N4 Z-scheme photocatalyst coupled with Fe3O4/H2O2 system for 2, 4-dimethylphenol degradation

In this study graphitic carbon nitride (g-C₃N₄ or GCN) and phosphorus doped graphitic carbon nitride (p-g-C₃N₄ or PCN) were prepared using facile thermal polycondensation method. Phosphorus doping was employed to preserve the non-metallic nature of GCN. The AgCl/PCN/Fe₃O₄ heterojunction was synthesized using a simple in-situ route. The photocatalytic performance of the GCN, PCN, Fe₃O₄ and AgCl/PCN/Fe₃O₄ was tested towards 2, 4-dimethylphenol (DMP) pollutant. The work explored improvement in physiochemical properties and reduction of band gap of GCN after P doping (through Tauc's plot method). Coupling with AgCl (silver halide) also enhanced photoinduced charge carriers' separation and migration ability due to apt band alignment among both AgCl and PCN photocatalysts which resulted in formation of direct Z-scheme charge transfer mechanism. Similarly, the incorporation of ferrimagnetic material i.e. Fe₃O₄ enhanced the generation of hydroxyl (^•OH) radicals via photo-Fenton process and facilitated photocatalysts easy separation from the aqueous medium. Through PL and EIS analysis the enhanced charge separation and migration ability in AgCl/PCN/Fe₃O₄ nanocomposite was validated. The attained DMP degradation efficiency of photo-Fenton assisted AgCl/PCN/Fe₃O₄/H₂O₂ Z-scheme nanocomposite was much higher i.e. 99% compared to other photocatalysts within 60 min of visible light irradiation following pseudo-first-order kinetics. Electron paramagnetic resonance (EPR) and scavenging tests confirmed the substantial role of ^•OH and ^•O₂^- radicals in the photo-Fenton reaction. Furthermore, liquid chromatography-mass spectrometry (LC-MS) analysis detected the generated oxidative products and mineralization pathways associated with DMP degradation. The proposed direct Z-scheme charge transfer route presented efficient charge separation and migration ability in AgCl/PCN/Fe₃O₄ nanocomposite. Recycle ability of the fabricated AgCl/PCN/Fe₃O₄ photocatalyst was tested up to 5 cycles with 90% removal efficacy, confirming the excellent reusability and stability of AgCl/PCN/Fe₃O₄ photocatalyst.

Visible-Light Activation of Persulfate or H2O2 by Fe2O3/TiO2 Immobilized on Glass Support for Photocatalytic Removal of Amoxicillin: Mechanism, Transformation Products, and Toxicity Assessment

Fe₂O₃/TiO₂ nanocomposites were fabricated via a facile impregnation/calcination technique employing different amounts iron (III) nitrate onto commercial TiO₂ (P25 Aeroxide). The as-prepared Fe₂O₃/TiO₂ nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDXS), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller analysis (BET), electron impedance spectroscopy (EIS), photoluminescence spectroscopy (PL), and diffuse reflectance spectroscopy (DRS). As a result, 5% (w/w) Fe₂O₃/TiO₂ achieved the highest photocatalytic activity in the slurry system and was successfully immobilized on glass support. Photocatalytic activity under visible-light irradiation was assessed by treating pharmaceutical amoxicillin (AMX) in the presence and absence of additional oxidants: hydrogen peroxide (H₂O₂) and persulfate salts (PS). The influence of pH and PS concentration on AMX conversion rate was established by means of statistical planning and response surface modeling. Results revealed optimum conditions of [S₂O₈^2-] = 1.873 mM and pH = 4.808; these were also utilized in presence of H₂O₂ instead of PS in long-term tests. The fastest AMX conversion possessing a zero-order rate constant of 1.51 × 10^-7 M·min^-1 was achieved with the photocatalysis + PS system. The AMX conversion pathway was established, and the evolution/conversion of formed intermediates was correlated with the changes in toxicity toward Vibrio fischeri. Reactive oxygen species (ROS) scavenging was also utilized to investigate the AMX conversion mechanism, revealing the major contribution of photogenerated h⁺ in all processes.

Fe3O4-TiO2 Thin Films in Solar Photocatalytic Processes

The optical properties of 5wt% Fe₃O₄-TiO₂ thin films were evaluated in detail with the aim of proposing a mechanism for solar photocatalytic processes and highlighting the advantages over the use of bare TiO₂. The results showed that the incorporation of 5wt% Fe₃O₄ enhanced the optical properties by a redshift to a wavelength in the visible range, reducing the anatase/rutile band gap energy from 3.2 eV to 2.8 eV. Photoluminescence studies reveal a superior separation efficiency of photoexcited electron-hole pairs when Fe₃O₄ nanoparticles (NPs) are present in the photocatalyst. X-ray photoelectron spectroscopy spectra confirm the presence of Fe₃O₄ and existence of a chemical bonding between TiO₂ and Fe₃O₄ NPs. Moreover, in this study, a mechanism of solar photocatalytic processes involving Fe₃O₄-TiO₂ thin films is proposed and it is supported by experimental results. Finally, solar photocatalytic experiments were carried out, indicating that the effectiveness for the removal of the selected pharmaceutical is considerably improved when the composite material is used as catalyst. Furthermore, it was demonstrated that the photocatalytic activity of the prepared Fe₃O₄-TiO₂ thin films depends on their thickness, achieving the highest pharmaceutical removal yields using the 2 µm thick sample. The stability and reusability of the catalyst was confirmed studying the photocatalytic activity over three cycles.

Two Copper-Containing Polyoxometalate-Based Metal-Organic Complexes as Heterogeneous Catalysts for the C-H Bond Oxidation of Benzylic Compounds and Olefin Epoxidation

Using a one-pot assembly method, two novel copper-containing Keggin-type polyoxometalates (POMs)-based metal-organic complexes, that is, [Cu^II₂(pbba)₂NO₃^-(H₂O)₂(PW₁₂O₄₀)]·3H₂O [PW₁₂-Cu-pbba, H₂pbba = 1,1'-(1,4-phenylene-bis(methylene))-bis(pyridine-3-carboxylic acid)] and [Cu^II₂(pbba)₂(H₂O)₂(GeW₁₂O₄₀)]·3H₂O (GeW₁₂-Cu-pbba), were successfully synthesized. These two complexes are isostructural, differing only in their POM components. They are applicable as heterogeneous catalysts for the C-H bond oxidation of benzylic compounds and olefin epoxidation under mild conditions, with oxygen as the oxidant and isobutyraldehyde as the coreductant. The catalytic activity of PW₁₂-Cu-pbba was superior to that of GeW₁₂-Cu-pbba. Under the optimal conditions, PW₁₂-Cu-pbba catalyzed the oxidation of indane into 1-indanone with an 81% yield and >99% selectivity within 48 h. As heterogeneous catalysts, both complexes demonstrated excellent recoverability and high stability and could be stably reused five times without significant activity loss.

Review on the preparation of fuels and chemicals based on lignin

Lignin is by far the most abundant natural renewable aromatic polymer in nature, and its reserves are second only to cellulose. In addition to the rich carbon content, the structure of lignin contains functional groups such as benzene rings, methoxyl groups, and phenolic hydroxyl groups. Lignin degradation has become one of the high value, high quality and high efficiency methods to convert lignin, which is of great significance to alleviating the current energy shortage and environmental crisis. This article introduces the hydrolysis methods of lignin in acidic, alkaline, ionic liquids and supercritical fluids, reviews the heating rate, the source of lignin species and the effects of heating rate on the pyrolysis of lignin, and briefly describes the metal catalysis, oxidation methods such as electrochemical degradation and photocatalytic oxidation, and degradation reduction methods using hydrogen and hydrogen supply reagents. The lignin degradation methods for the preparation of fuels and chemicals are systematically summarized. The advantages and disadvantages of different methods, the selectivity under different conditions and the degradation efficiency of different catalytic combination systems are compared. In this paper, a new approach to improve the degradation efficiency is envisioned in order to contribute to the efficient utilization and high value conversion of lignin.

Comparative degradation of 5-fluorouracil in aqueous solution by using H2O2-modified subcritical water, photocatalytic oxidation and electro-Fenton processes

This study investigated the degradation of the antineoplastic agent 5-fluorouracil (5-FU) widely applied to treat different cancers using different advanced oxidation processes such as electro-Fenton (EF), photocatalysis with TiO_2, and H₂O₂-modified subcritical water oxidation. The treatment with the EF process was the most efficient compared to others. Interestingly, in the EF process, the oxidative degradation of 5-FU behaved differently depending on the anode used. At low currents (20 and 40 mA), Pt and DSA anodes performed better than BDD and Ti₄O₇ anodes. In contrast, at the higher current of 120 mA, the production of heterogeneous hydroxyl radicals (M(^•OH)) became important and contributed significantly to the oxidation of 5-FU in addition to homogeneous ^•OH generated in the bulk solution. These latter have high O₂-evolution overpotential leading to the high amount of physisorbed M(^•OH) compared to Pt and DSA. The oxidative degradation of 5-FU was then performed by titanium dioxide-based photocatalytic oxidation and subcritical water oxidation processes, both of which showed a lower degradation efficiency and failed to achieve complete mineralization. Finally, a comparison was performed in laboratory-scale, taking into account the following performance indicators: the degradation efficiency, the mineralization power, the cost of equipment and reagents, and the energy required for the treatment of 5-FU.

Synthesis, characterization, and application of α-Fe2 O3 @TiO2 @SO3 H photo-Fenton catalyst for photocatalytic degradation of biologically pre-treated wood industry wastewater

The efficiency of removing chemical oxygen demand (COD) and turbidity from wood wastewater was investigated using a sequencing batch reactor (SBR) and the photo-Fenton process. A total of 94.78% of COD reduction and 99.9% of turbidity removal were observed under optimum conditions of SBR, which consisted of an organic loading rate (OLR) of 0.453 kg COD m^-3  day^-1 , mixed liquor suspended solids (MLSS) of 4564 mg L^-1 , and cycle time of 48 h. A magnetic α-Fe₂ O₃ @TiO₂ @SO₃ H nanocatalyst was prepared as a heterogeneous Fenton reagent. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalyst. The response surface methodology (RSM) was used to optimize the process based on a central composite design (CCD). The maximum photocatalytic degradation of 87.54% and COD reduction of 83.35% were achieved at a dosage of 0.6 g L^-1 of catalyst, 30 mg L^-1 of H₂ O₂ , and pH of 3.5 for 45 min. The results indicated that a combination of the SBR process and α-Fe₂ O₃ @TiO₂ @SO₃ H could be used as an effective method for the treatment of wood wastewater. PRACTITIONER POINTS: A combination of the SBR and photo-Fenton process was introduced as an impressive method for wood industry wastewater treatment. The efficiencies of COD, BOD₅ , NO₃ -N, PO₄ -P, and color removal were obtained according to the standard limits in Iran. To our knowledge, this study is the first report of the use of synthesized α-Fe₂ O₃ @TiO₂ @SO₃ H photocatalyst for the wood industry wastewater treatment.

Integration of coagulation-flocculation and heterogeneous photocatalysis for the treatment of pulp and paper mill effluent

A two-step process involving coagulation-flocculation followed by solar photocatalysis - based Advanced Oxidation Process (AOP) using TiO₂-Reduced Graphene Oxide (TRGO) nanocomposite as catalyst has been employed for the treatment of pulp and paper mill effluent. As the effluent is loaded with a high amount of organics with initial chemical oxygen demand (COD) as high as 3516, a pre-treatment is required before applying photocatalytic treatment. Coagulation-flocculation was identified as an effective pre-treatment strategy. Among the various coagulants tested, CuSO₄.5H₂O showed the best % COD reduction of 84 at pH 6, at a loading of 5 g/L. The primary treatment of coagulation improved the biodegradability index from 0.23 to 0.37. TRGO photocatalyst, employed in the second stage of photocatalytic treatment was synthesised by an ultrasound assisted solvothermal method and well characterised by various spectroscopic/analytical tools. The composite was found to be an efficient solar photocatalyst and achieved 1.76 and 2.1 times more COD reduction than synthesised TiO₂ and commercial P25 respectively. The final effluent after the combined treatment was neutral and the biochemical oxygen demand (BOD) and COD were 11.7 and 120 mg/L respectively which were below the given limit of National Environmental Quality Standards.

Photocatalytic degradation of 2,4-DNT in simulated wastewater by magnetic CoFe2O4/SiO2/TiO2 nanoparticles

Discharge of 2,4-dinitrotoluene (2,4-DNT) into the environment leads to a serious soil and water sources pollution problem, due to toxicity and possible carcinogenicity of this toxic substance. In this work, the photocatalytic degradation of 2,4-DNT was investigated using CoFe₂O₄/SiO₂/TiO₂ nanoparticles. The catalyst features were characterized by using XRD, TEM, EDX, UV-vis DRS, FTIR, and VSM techniques. The influence of different experimental factors on degradation efficiency including pH value, catalyst dosages, and initiate concentration of 2,4-DNT were investigated. Mineralization of the model pollutant was determined using TOC analysis under optimum conditions. A possible mechanism, process kinetic and reusability of magnetic photocatalyst were also performed. In optimum experimental conditions (pH=3, photocatalyst dosage=0.75 g/L, 2,4-DNT=0.025 g/L), degradation efficiency achieved 88.5% within 180-min reaction time with TOC removal of 55.6%. Dominate oxidizing radicals during the degradation of 2,4-DNT by CoFe₂O₄/SiO₂/TiO₂ were hydroxyl radicals. The photocatalytic degradation of 2,4-DNT followed first-order rate kinetics. After three successive use cycles, the degradation efficiency was reduced by 64%. Our results revealed that the synthesized CoFe₂O₄/SiO₂/TiO₂ photocatalyst was a good choice for degradation of 2,4-DNT, due to proper potential reusability and catalytic activity.

Preparation and application of α-Fe2O3@TiO2@SO3H for photocatalytic degradation and COD reduction of woodchips industry wastewater

In this study, we investigated the efficiency of photocatalytic degradation and chemical oxygen demand (COD) reduction from woodchips industry wastewater using α-Fe₂O₃@TiO₂@SO₃H. A magnetic α-Fe₂O₃@TiO₂@SO₃H was prepared as a heterogeneous photo-Fenton catalyst. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalysts. The response surface methodology (RSM) was used to optimize the photo-Fenton process based on a Box-Behnken design (BBD). The parameters such as catalyst dosage, H₂O₂ dosage, pH, and contact time on photocatalytic degradation and the reduction of COD were studied. The maximum photocatalytic degradation of 93.75% and COD reduction of 86.54% were achieved at a dosage of the catalyst of 1 g L^-1, H₂O₂ dosage of 40 mg L^-1, and a pH of 3.5 at 45 min. The kinetics of the photo-Fenton process was studied for the woodchips wastewater treatment under optimum conditions. The pseudo-second-order kinetic model for photocatalytic degradation and COD reduction was obtained. The results indicated that a α-Fe₂O₃@TiO₂@SO₃H could be used as an effective heterogeneous photocatalyst for the treatment of woodchips industry wastewater. Preparation and application of α-Fe₂O₃@TiO₂@SO₃H for photocatalytic degradation and COD reduction of woodchips industry wastewater.

Differential evolution-based optimization of corn stalks black liquor decolorization using active carbon and TiO2/UV

In this work, the active carbon adsorption and TiO₂/UV decolorization of black liquor were studied through experimental analysis (planned using Design of Experiments), modelling and optimization (with Response Surface Method and Differential Evolution). The aim is to highlight the importance of optimization methods for increasing process efficiency. For active carbon adsorption, the considered process parameters were: quantity of active carbon, dilution, and contact time. For TiO₂ promoted photochemical decolorization the process parameters were: TiO₂ concentration, UV path length and irradiation time. The determined models had an R squared of 93.82% for active carbon adsorption and of 92.82% for TiO₂/UV decolorization. The optimization of active carbon resulted in an improvement from 83.08% (corresponding to 50 g/L quantity of active carbon, 30 min contact time and 200 dilution) to 100% (corresponding to multiple combinations). The optimization of TiO₂/UV decolorization indicated an increase of efficiency from 36.63% (corresponding to 1 g/L TiO₂ concentration, 60 min irradiation time and 5 cm UV path length) to 46.83% (corresponding to 0.4 g/L TiO₂ concentration, 59.99 min irradiation time and 2.85 cm UV path length). These results show that the experiments and the subsequent standard RSM optimization can be further improved, leading to better performance.

Magnetic photocatalysts from δ-FeOOH and TiO2 and application in reactions for degradation of methylene blue and paracetamol with UV-C and sunlight

Water contamination is a common problem, especially considering dyes and drugs disposal. A possible and effective treatment method to remove these organic pollutants from water is photocatalytic reaction. This study aimed to improve the photocatalytic properties of TiO₂ using iron oxides (Ti/Fe composite). Different magnetic photocatalysts based on commercial TiO₂ were obtained with 30, 50, and 80% (wt./wt.) of TiO₂ supported on maghemite. X-ray diffraction with Rietveld refinement confirms the presence of γ-Fe₂O₃, α-Fe₂O₃, anatase, and rutile, as well as the relative percentages of the phases present in each photocatalyst. The magnetic properties were certified by VSM and sedimentation kinetics in the presence of a magnetic field. Besides their magnetic properties, UV-vis DRS shows that the obtained photocatalysts presented lower bandgap values when compared with TiO₂. These factors allowed the materials to absorb radiation in the visible-light region and the separation from the reaction medium by the application of magnetic field. It was observed an enhancement of photodegradation reaction of methylene blue (MB) and paracetamol (PC). For example, when the content of TiO₂ increased from 30 to 80% (wt./wt.), the efficiency increased from 58 to 99% (for MB) and 39 for 80% (for PC) under UV (λ = 254 nm). The reactions carried out with solar radiation showed 56 to 95% efficiency to discolor MB. In addition, the results of sedimentation kinetics and characterization confirmed the goals of the synthesis.

A Copper-Containing Polyoxometalate-Based Metal-Organic Framework as an Efficient Catalyst for Selective Catalytic Oxidation of Alkylbenzenes

A copper-containing polyoxometalate-based metal-organic framework (POMOF), Cu^I₁₂Cl₂(trz)₈[HPW₁₂O₄₀] (HENU-7, HENU = Henan University; trz = 1,2,4-triazole), has been successfully synthesized and well-characterized. In addition, the excellent catalytic ability of HENU-7 has been proved by the selective oxidation of diphenylmethane. Under the optimal conditions, the diphenylmethane conversion obtained over HENU-7 is 96%, while the selectivity to benzophenone is 99%, which outperforms most noble-metal-free POM-based catalysts. Moreover, HENU-7 is stable to reuse for five runs without an obvious loss in activity and also can catalyze the oxidation of different benzylic C-H with satisfactory conversions and selectivities, which implied the significant catalytic activity and recyclability.

Pollutants removals and energy consumption in electrochemical cell for pulping processes wastewater treatment: Artificial neural network, response surface methodology and kinetic studies

Response surface methodology (RSM) and artificial neural network (ANN) were used for modelling the electrocoagulation removal of pollutants from wastewater from pulping processes. The Design of Experiment based on central composite design was used to investigate the combine effects of pH (5.4-9.0), time (10-45 min) and current density (j) (9-39 mA/m²), on the removal efficiency of the Chemical Oxygen Demand (COD), Total Dissolve Solids (TDS) as well as Turbidity while Energy consumption (EC) was estimated per kg [COD] removed. The kinetics of the process was modelled with pseudo first and second order models. The removability of the COD, TDS and Turbidity were found to be 76.4, 57.0 and 97.13% with Energy consumption of 2.72 kWh/kg_[COD] at optimal pH 6.83, current density of 22.06 mA/m², and reaction time of 45 min. The ANN model gave a better fitting of the electrocoagulation process than the RSM, considering the R² of 0.999 and MSE of 0.00753 obtained for the former. The pseudo first order model gave a better analysis of the kinetic data. The characterization of the sludge produced showed the potential of its use as adsorbent for organic or mineral contaminants and recovery of aluminium and other metals. Thus, electrocoagulation with monopolar aluminium electrodes displayed effective and a viable alternative for the pollutants removal from pulp processing wastewater.

The Cramer's rule for the parametrization of phenol and its hydroxylated byproducts: UV spectroscopy vs. high performance liquid chromatography

A linear algebra theorem like Cramer's rule was used for the analysis of a system of equations obtained from UV spectroscopy, and results were compared against those obtained from HPLC analysis. This parametrization allowed to quantify the concentration of the main intermediate products detected along the photodegradation of phenol under UV-Vis irradiation of TiO₂. UV spectroscopy data for phenol, hydroquinone, and benzoquinone were analyzed using the Cramer's rule. The overlapping interference of the intermediate products in the UV spectra was corrected. It can be concluded that the Cramer's rule can be used for the parametrization of the UV absorbance data of phenol and its main intermediate products. This methodology permitted to obtain the concentration of phenol and their intermediate products by UV-visible with a high precision in comparison of HPLC. The parametrization showed a correlation coefficient of ca. 0.9775 between the phenol concentration obtained by UV spectroscopy and values obtained from HPLC analysis. In this sense, results can be considered with good precision, and accordingly, it can be concluded that the methodology is reliable, and UV-visible spectroscopy can be selected instead of HPLC in much of the experiments concerning with aqueous-phase reactions.

Photocatalytic removal of eosin dye from aqueous solution over titanium dioxide

A Various concentrations of Eosin dye were irradiated using titanium dioxide as a catalyst. The irradiation was carried out using the catalyst (0.1gm/100ml), mercury lamp 125 Watts from external source and at Rt. The effect of TiO2 on the photocatalytic degradation of Eosin was studied in various conditions such as, studying the effect of loaded mass of titanium dioxide, effect of eosin dye concentration and effect of inorganic anions.

Mechanochemical synthesis of nanophotocatalysts SiO2/TiO2/Fe2O3: their structural, thermal and photocatalytic properties

In the study the mechanochemical synthesis was used to prepare photocatalytic materials based on TiO2, SiO2, and Fe2O3. During the preparation the impact of composition, milling speed, and calcination process on the properties of the composites was investigated. The structural and thermal properties of photocatalysts were determined using the N2 adsorption/desorption, XRD, and FT-IR/PAS methods. The thermal stability of the obtained materials was also examined (TG/DTG). Moreover, their photocatalytic activity was tested in relation to Methylene Blue at UV and Vis radiation. The results indicate that the mechanochemical synthesis in the high-energy planetary mill is an effective method for obtaining materials with photocatalytic properties at the UV and Vis radiation. It was shown that the removal process of MB may be described by the pseudo-first-order kinetics.

Photocatalytic degradation of swine wastewater on aqueous TiO2 suspensions: optimization and modeling via Box-Behnken design

Heterogeneous photocatalysis is a promising technology to treat many industrial wastewaters. To date, this potential has not been proven with wastewaters from agricultural origins, such as swine wastewater. In this work, the photocatalytic degradation of swine wastewater was studied by applying a response surface methodology based on the Box-Behnken design. The interactive effects of the variation of factors such as photocatalyst dosage (X₁), wastewater concentration (X₂), and irradiation time (X₃) were analyzed to identify the optimal operating conditions for COD reduction. A second-order polynomial accurately represented organics degradation with a high adjusted R-squared (0.9666). The main effects of factor X₂ and the quadratic effects of factors X₂ and X₃ were the most significant for COD reduction. The optimal conditions for COD degradation were 1.16 g L⁻¹ for photocatalyst dosage, 1.68% for wastewater concentration, and irradiation time of 9.2 h. These results have been validated in a confirmation experiment and COD removal reached 91.7% (98.1 % predicted). Based on the Langmuir—Hinshelwood model, the reaction rate constant was 3.9×10⁻³ min⁻¹. Besides, FTIR analysis indicated that Aeroxide® TiO₂ reusability may be possible, especially for low wastewater concentrations. Heterogeneous photocatalysis can be applied as a technology for the integrated treatment of industrial wastewaters resulting from swine production.

Molecular Composition of Size-Fractionated Fulvic Acid-Like Substances Extracted from Spent Cooking Liquor and Its Relationship with Biological Activity

The treatment of spent cooking liquor is critical for clean production of pulp and paper industry. There is a compelling need to develop a cost-effective and green technology for reuse of organic matter in spent cooking liquor to mitigate the negative impacts on the environment. The objective of this study is to examine the chemical structure of fulvic acid-like substances extracted from spent cooking liquor (PFA) and their relationship with bioactivity in plant growth. Compared with the benchmark Pahokee peat fulvic acid (PPFA), PFA has less aromatic structure, but higher content of lignin, carbohydrates, and amino acid. After fractionation, protein/amino proportion decreased with increasing molecular weight, but the aromaticity increased. Under salt stress, rice seedling growth was promoted by PFA with low molecular weight (<5 kDa), but inhibited by fraction with high molecular weight (>10 kDa). Principal component analysis suggested that promoted growth was more related with chemical structure (O- and N-alkyl moieties) than with molecular weight. This study provided the theoretical basis for development of an innovative green technology of sustainable reuse of spent cooking liquor in agriculture.

Photoelectrocatalytic decolorization of methylene blue using reduced graphene oxide modified TiO2 on filter paper

In this work, titanium dioxide (TiO₂) was modified with reduced graphene oxide (rGO), and then coated on filter paper to prepare the rGT/FP photoelectrode for the photoelectrocatalytic (PEC) decolorization of methylene blue (MB). The physicochemical properties of the rGT/FP photoelectrode were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and UV-Vis diffuse reflectance spectroscopy (DRS). The decolorization results demonstrated that the photocatalytic (PC) and electrocatalytic (EC) efficiency of the photoelectrode could be significantly improved by the modification of rGO. The improvement of PC and EC efficiency might attribute to the existence of rGO, which could extend the light-harvesting efficiency, promote the photocurrent response value and suppress the charge recombination. Furthermore, the PEC decolorization of MB using the rGT/FP photoelectrode presented higher efficiency than the sum of PC and EC decolorization, indicating the synergistic effect between the photo and electrical energy.

Wafer-Scale Fabrication of Sub-10 nm TiO2-Ga2O3 n-p Heterojunctions with Efficient Photocatalytic Activity by Atomic Layer Deposition

Wafer-scale, conformal, two-dimensional (2D) TiO₂-Ga₂O₃ n-p heterostructures with a thickness of less than 10 nm were fabricated on the Si/SiO₂ substrates by the atomic layer deposition (ALD) technique for the first time with subsequent post-deposition annealing at a temperature of 250 °C. The best deposition parameters were established. The structure and morphology of 2D TiO₂-Ga₂O₃ n-p heterostructures were characterized by the scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), etc. 2D TiO₂-Ga₂O₃ n-p heterostructures demonstrated efficient photocatalytic activity towards methyl orange (MO) degradation at the UV light (λ = 254 nm) irradiation. The improvement of TiO₂-Ga₂O₃ n-p heterostructure capabilities is due to the development of the defects on Ga₂O₃-TiO₂ interface, which were able to trap electrons faster.

Photocatalytic hydrogen production by strontium titanate-based perovskite doped europium (Sr0.97Eu0.02Zr0.1Ti0.9O3)

The aim of the present research was to study the photocatalytic activity under UV/visible irradiation of the ceramic compound Sr_0.97Eu_0.02Zr_0.1Ti_0.9O₃ (SEZT1) using ethylenediaminetetraacetic acid (EDTA) as a sacrificial agent to produce H₂. The effects of the reaction parameters such as pH, the initial concentration of the sacrificial agent, and the amount of photocatalyst were systematically investigated through response surface methodology. The results showed that the photocatalytic performance was strongly affected by higher levels of sacrificial agent concentration (70.0 mM EDTA) and by low amounts of photocatalyst SEZT1 (0.01 g/L as catalyst loading) at alkaline conditions (pH 9.0) after 5 h of UV irradiation (6140.04 μmol), using Eu-doped strontium zirconate titanate as semiconductor.

Phosphorus removal and recovery from fosfomycin pharmaceutical wastewater by the induced crystallization process

The excessive release of phosphorus is a main cause of eutrophication, but phosphorus itself is an important non-renewable resource. If phosphorus could be recovered from wastewater, it can not only reduce the pollution, but also reach the aim of resource recycle. An induced crystallization process was combined with the schorl/H₂O₂ system to remove and recover phosphorus from the fosfomycin pharmaceutical wastewater. Firstly, in the schorl/H₂O₂ heterogeneous Fenton system, the organic phosphorus (OP) in fosfomycin pharmaceutical wastewater was transformed to the inorganic phosphorus (IP), and then IP was recovered by hydroxyapatite (HAP) induced crystallization process. In sequence batch reactors (SBR), the entire crystallization process went through 60 cycles, and each of the cycle lasted for 12 h, including 2 h for reaction and 10 h for sedimentation. The influence of different initial pH values, which were 8, 9, 10 and 11, on the induced crystallized product was investigated. The morphology and structure of the induced crystallized product were analysed. The results indicated that when the pH value was about 8, most of the recovery products was in the form of dicalcium phosphate anhydrous (DCP, CaHPO₄). At pH 9 the recovery products were mainly DCP and HAP. As pH increased to 10 or 11, most of the recovery products would be HAP and calcium carbonate. Carbonate involved in the crystallization reaction, especially at pH 11.

Nitric acid-anionic surfactant modified activated carbon to enhance cadmium(II) removal from wastewater: preparation conditions and physicochemical properties

The authors used a nitric acid (HNO₃)-sodium dodecyl benzene sulfonate (SDBS) method to modify a lignite-based activated carbon. These modified carbons were appraised for their removal of Cd(II) from aqueous solutions. Response surface methodology was employed to optimize the preparation factors including nitric acid concentration C_N, temperature T and SDBS concentration C_S. Statistical analysis indicated that the interaction of C_N and C_S incurred the most effect on the maximum cadmium adsorption capacity (Q_m). The optimal Q_m appeared at C_N = 3.29 mol/L, T = 76 °C and C_S=30,700 mg/L. The optimal protocol achieved 44.21 mg/g Q_m for Cd(II) which was about 7 times larger than for this pristine lignite activated carbon (LAC) (6.78 mg/g). The physical-chemical properties of the modified activated carbons following each synthesis step were characterized relative to their surface area, oxygen functionality, and external surface charge. It was confirmed that the developed surface area, functional groups and negative charges were mainly responsible for the higher adsorption capacity for the LAC that have been more favorably tailored by this HNO₃-SDBS protocol.

Photocatalytic degradation of sulfamethoxazole by hierarchical magnetic ZnO@g-C3N4: RSM optimization, kinetic study, reaction pathway and toxicity evaluation

The degradation of sulfamethoxazole (SMX) by a synthesized hierarchical magnetic zinc oxide based composite ZnO@g-C₃N₄ (FZG) was examined. Hierarchical FZG was synthesized by using Fe₃O₄ nanoparticle as the magnetic core and urea as the precursor for in situ growth of g-C₃N₄ on the surface of petal-like ZnO. The effect of catalyst dosage (0.4-0.8 g/L), solution pH (3-11) and airflow rate (0.5-2.5 L/min) on the SMX removal efficiency and the optimization of process was studied by response surface methodology (RSM) based on central composite design (CCD). The obtained RSM model with R² = 0.9896 showed a satisfactory correlation between the predicted values and experimental results of SMX removal. Under the optimum conditions, i.e. 0.65 g/L photocatalyst concentration, pH = 5.6 and airflow rate = 1.89 L/min, 90.4% SMX removal was achieved after 60 min reaction. The first-order kinetic rate constant for SMX removal by using FZG was 0.0384 min^-1 while the rate constant by commercial ZnO was 0.0165 min^-1. Moreover, under the optimum conditions, about 64% COD removal and 45% TOC removal and a considerable reduction in toxicity were observed. The analysis of generated intermediates during the photocatalytic degradation of SMX was conducted by LC-HR-MS/MS method and a degradation pathway was proposed.

Photocatalytic Treatment of An Actual Confectionery Wastewater Using Ag/TiO2/Fe2O3: Optimization of Photocatalytic Reactions Using Surface Response Methodology

Titanium dioxide (TiO2) photocatalysis is one of the most commonly studied advanced oxidation processes (AOPs) for the mineralization of deleterious and recalcitrant compounds present in wastewater as it is stable, inexpensive, and effective. Out of all, doping with metal and non-metals, and the heterojunction with another semiconductor were proven to be efficient methods in enhancing the degradation of organic pollutants under ultraviolet (UV) and visible light. However, complex degradation processes in the treatment of an actual wastewater are difficult to model and optimize. In the present study, the application of a modified photocatalyst, Ag/TiO2/Fe2O3, for the degradation of an actual confectionery wastewater was investigated. Factorial studies and statistical design of experiments using the Box-Behnken method along with response surface methodology (RSM) were employed to identify the individual and cross-factor effects of independent parameters, including light wavelength (nm), photocatalyst concentration (g/L), initial pH, and initial total organic carbon (TOC) concentration (g/L). The maximum TOC removal at optimum conditions of light wavelength (254 nm), pH (4.68), photocatalyst dosage (480 mg/L), and initial TOC concentration (11,126.5 mg/L) was determined through the numerical optimization method (9.78%) and validated with experimental data (9.42%). Finally, the first-order rate constant with respect to TOC was found to be 0.0005 min−1 with a residual value of 0.998.

Magnetically Recyclable Fe3O4@Zn xCd1- xS Core-Shell Microspheres for Visible Light-Mediated Photocatalysis

Magnetically recyclable photocatalyst has drawn considerable research interest because of its importance in practical applications. Herein, we demonstrate a facile hydrothermal process to fabricate magnetic core-shell microspheres of Fe₃O₄@Zn _xCd_{1- x}S, successfully using Fe₃O₄@ZnS core-shell microspheres as sacrificed templates. The as-prepared magnetically recyclable photocatalysts show efficient photochemical reduction of Cr(VI) under irradiation of visible light. The photochemical reduction mechanism has been studied to illustrate the reduction-oxidation ability of the photogenerated electrons (e^-) and holes (h⁺), which play an important role in the reduction of Cr(VI) to Cr(III) and oxidation of organic dyes. The as-prepared Fe₃O₄@Zn_0.55Cd_0.45S core-shell microspheres show good chemical stability and only a slight decrease in the photocatalytic activity after four recycles. In particular, the as-prepared photocatalysts could be easily recycled and reused by an external magnetic field. Therefore, this work would provide a facile chemical approach for controlled synthesis of magnetic nanostructures combined with alloyed semiconductor photocatalysts for wastewater treatment.

Effect of Zinc Acetate Concentration on Optimization of Photocatalytic Activity of p-Co3O4/n-ZnO Heterostructures

In this work, p-Co₃O₄/n-ZnO heterostructures were fabricated on Ni substrate by hydrothermal-decomposition method using cobaltous nitrate hexahydrate (Co(NO₃)₂·6H₂O) and zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) as precursors with zinc acetate concentration varying from 5.0 to 55.0 mM. Structure and morphology of the developed samples were characterized by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Effect of zinc acetate concentration on the photocatalytic activity of p-Co₃O₄/n-ZnO heterostructures was investigated by degradation of methyl orange (MO) under the UV light irradiation. The fabricated p-Co₃O₄/n-ZnO heterostructures exhibited higher photocatalytic activity than pure Co₃O₄ particles. In order to obtain the maximum photocatalytic activity, zinc acetate concentration was optimized. Specifically, at 35 mM of zinc acetate, the p-Co₃O₄/n-ZnO showed the highest photocatalytic activity with the degradation efficiency of MO reaching 89.38% after 72 h irradiation. The improvement of photocatalytic performance of p-Co₃O₄/n-ZnO heterostructures is due to the increased concentration of photo-generated holes on Co₃O₄ surface and the higher surface-to-volume ratio in the hierarchical structure formed by nano-lamellas.

The first morphologically controlled synthesis of a nanocomposite of graphene oxide with cobalt tin oxide nanoparticles

In the present research, the degradation and decolorization of Reactive Black 5 synthetic dye at 30 ppm concentration under sun irradiation in the presence of a newly synthesized graphene based cobalt tin oxide nanocomposite were investigated. These nanoparticles were synthesized by a simple hydrothermal approach using precursor chloride salt i.e., stannous chloride and cobalt chloride and then adsorbed on the surface of RGO by a solvothermal process by changing the condition. The newly synthesized product was subjected to various instrumentation to study the morphology and other properties. X-ray powder diffraction analysis (XRD) explained the structural composition and various parameters of the product, which were further verified by Vesta software. The surface morphology of the product was analyzed by scanning electron microscopy (SEM) and it was observed that the size of each cube was approximately 5–10 μm from every face of the cube. Transmission electron microscopy (TEM) explained that the nanoparticles were within the range of 100–250 nm. These synthesized nanocubes were used in one more application, which was the investigation of the fuel efficiency in the presence of different concentrations of newly synthesized nanocomposites as a catalyst. The efficiency of kerosene oil was investigated by studying different parameters: the flash point, fire point, specific gravity, cloud point, pour point, and calorific value at increasing dosages of catalyst (0, 30, 60 and 90 ppm). It was observed that the values of these parameters changed significantly by changing the concentration of the catalyst dosage. The effect of the nanoparticles on the degradation of the RB 5 azo dye showed the highest removal percentage at the largest value of catalyst dosage, which was 0.70 mg ml⁻¹ with the highest value of 3 ml of hydrogen peroxide.

Tin cobalt hydroxide nanoparticles were synthesized by a simple hydrothermal technique. A graphene based cobalt tin oxide nanocomposite was synthesized by a solvothermal method.

Fabrication of magnetically separable NiFe2O4/BiOI nanocomposites with enhanced photocatalytic performance under visible-light irradiation

SEM image of as-synthesized NiFe₂O₄/BiOI (NFO/BOI) nanocomposites (a) and schematic illustration of excitation and separation of photo-induced electron–hole pairs for NFO/BOI nanocomposites (b).

High photocatalytic activity of Fe2O3/TiO2 nanocomposites prepared by photodeposition for degradation of 2,4-dichlorophenoxyacetic acid

Two series of Fe₂O₃/TiO₂ samples were prepared via impregnation and photodeposition methods. The effect of preparation method on the properties and performance of Fe₂O₃/TiO₂ for photocatalytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under UV light irradiation was examined. The Fe₂O₃/TiO₂ nanocomposites prepared by impregnation showed lower activity than the unmodified TiO₂, mainly due to lower specific surface area caused by heat treatment. On the other hand, the Fe₂O₃/TiO₂ nanocomposites prepared by photodeposition showed higher photocatalytic activity than the unmodified TiO₂. Three times higher photocatalytic activity was obtained on the best photocatalyst, Fe₂O₃(0.5)/TiO₂. The improved activity of TiO₂ after photodeposition of Fe₂O₃ was contributed to the formation of a heterojunction between the Fe₂O₃ and TiO₂ nanoparticles that improved charge transfer and suppressed electron-hole recombination. A further investigation on the role of the active species on Fe₂O₃/TiO₂ confirmed that the crucial active species were both holes and superoxide radicals. The Fe₂O₃(0.5)/TiO₂ sample also showed good stability and reusability, suggesting its potential for water purification applications.

Effect of adding brewery wastewater to pulp and paper mill effluent to enhance the photofermentation process: wastewater characteristics, biohydrogen production, overall performance, and kinetic modeling

Although a significant amount of brewery wastewater (BW) is generated during beer production, the nutrients in the BW could be reused as a potential bio-resource for biohydrogen production. Therefore, improvements in photofermentative biohydrogen production due to a combination of BW and pulp and paper mill effluent (PPME) as a mixed production medium were investigated comprehensively in this study. The experimental results showed that both the biohydrogen yield and the chemical oxygen demand removal were improved through the combination of BW and PPME. The best biohydrogen yield of 0.69 mol H₂/L medium was obtained using the combination of 10 % BW + 90 % PPME (10B90P), while the reuse of the wastewater alone (100 % BW and 100 % PPME) resulted in 42.3 and 44.0 % less biohydrogen yields than the highest yield, respectively. The greatest light efficiency was 1.97 % and was also achieved using the combination of both wastewaters at 10B90P. This study revealed the potential of reusing and combining two different effluents together, in which the combination of BW and PPME improved the nutrients and light penetration into the mixed production medium.

Degradation of ciprofloxacin by TiO2/Fe2O3/zeolite catalyst-activated persulfate under visible LED light irradiation

The (4)TiFeZ catalyst exhibited better performance for CIP removal compared with the other samples. The CIP was completely degraded in 120 min by using 1 g L⁻¹ (4)TiFeZ and 5.0 mM PS at pH 7.0.