Photodegradation of methylene blue and some emerging pharmaceutical micropollutants with an aqueous suspension of WZnO-NH2@H3PW12O40 nanocomposite

A critical review and bibliometric analysis of methylene blue adsorption using leaves

The rapid development of the industrial world causes wastewater containing dyes to continue to increase. Even in recent years, the food, textile, cosmetic, plastic, and printing industries have developed the use of dyes. Methylene blue (MB) is one of the cationic dyes widely used in dyeing silk, wood, and cotton because of its absorbency and good fastness to materials. The adsorption process is the best technique and preferred in removing dyes from wastewater due to excellent selectivity, high efficiency from high-quality treated effluent, flexibility in design, and simplicity. Therefore, there is a growing interest to identify low-cost alternative adsorbents that have reasonable adsorption efficiency, especially natural materials such as leaves. In this study, research on MB adsorption using leaves was analyzed using bibliometric analysis. Information of bibliometric is extracted from the Scopus database with the keyword "Methylene Blue", "Adsorption or Desorption", and "Leaves or leaf". The results showed that India, Desalination and Water Treatment, and SASTRA Deemed University were the country, journal, and institution that contributed the most publications on this topic. Therefore, it is expected that with the use of bibliometrics, the use of leaf-based MB adsorption processes in their potential for MB dye removal can be investigated especially for large-scale development.

Magnetic Activated Carbon from ZnCl2 and FeCl3 Coactivation of Lotus Seedpod: One-Pot Preparation, Characterization, and Catalytic Activity towards Robust Degradation of Acid Orange 10

Lotus seedpods (LSPs) are an abundant and underutilized agricultural residue discarded from lotus seed production. In this study, ZnCl₂ and FeCl₃ coactivation of LSP for one-pot preparation of magnetic activated carbon (MAC) was explored for the first time. X-ray diffraction (XRD) results showed that Fe₃O₄, Fe⁰, and ZnO crystals were formed in the LSP-derived carbon matrix. Notably, transmission electron microscopy (TEM) images showed that the shapes of these components consisted of not only nanoparticles but also nanowires. Fe and Zn contents in MAC determined by atomic absorption spectroscopy (AAS) were 6.89 and 3.94 wt%, respectively. Moreover, S_BET and V_total of MAC prepared by coactivation with ZnCl₂ and FeCl₃ were 1080 m²/g and 0.51 cm³/g, which were much higher than those prepared by single activation with FeCl₃ (274 m²/g and 0.14 cm³/g) or ZnCl₂ (369 m²/g and 0.21 cm³/g). MAC was subsequently applied as an oxidation catalyst for Fenton-like degradation of acid orange 10 (AO10). As a result, 0.20 g/L MAC could partially remove AO10 (100 ppm) with an adsorption capacity of 78.4 mg/g at pH 3.0. When 350 ppm H₂O₂ was further added, AO10 was decolorized rapidly, nearly complete within 30 min, and 66% of the COD was removed in 120 min. The potent catalytic performance of MAC might come from the synergistic effect of Fe⁰ and Fe₃O₄ nanocrystals in the porous carbon support. MAC also demonstrated effective stability and reusability after five consecutive cycles, when total AO10 removal at 20 min of H₂O₂ addition slightly decreased from 93.9 ± 0.9% to 86.3 ± 0.8% and minimal iron leaching of 1.14 to 1.19 mg/L was detected. Interestingly, the MAC catalyst with a saturation magnetization of 3.6 emu/g was easily separated from the treated mixture for the next cycle. Overall, these findings demonstrate that magnetic activated carbon prepared from ZnCl₂ and FeCl₃ coactivation of lotus seedpod waste can be a low-cost catalyst for rapid degradation of acid orange 10.

Electrochemical Sensing of H2O2 by Employing a Flexible Fe3O4/Graphene/Carbon Cloth as Working Electrode

We report the synthesis of Fe₃O₄/graphene (Fe₃O₄/Gr) nanocomposite for highly selective and highly sensitive peroxide sensor application. The nanocomposites were produced by a modified co-precipitation method. Further, structural, chemical, and morphological characterization of the Fe₃O₄/Gr was investigated by standard characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and high-resolution TEM (HRTEM), Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The average crystal size of Fe₃O₄ nanoparticles was calculated as 14.5 nm. Moreover, nanocomposite (Fe₃O₄/Gr) was employed to fabricate the flexible electrode using polymeric carbon fiber cloth or carbon cloth (pCFC or CC) as support. The electrochemical performance of as-fabricated Fe₃O₄/Gr/CC was evaluated toward H₂O₂ with excellent electrocatalytic activity. It was found that Fe₃O₄/Gr/CC-based electrodes show a good linear range, high sensitivity, and a low detection limit for H₂O₂ detection. The linear range for the optimized sensor was found to be in the range of 10-110 μM and limit of detection was calculated as 4.79 μM with a sensitivity of 0.037 µA μM^-1 cm^-2. The cost-effective materials used in this work as compared to noble metals provide satisfactory results. As well as showing high stability, the proposed biosensor is also highly reproducible.

Ozone-enhanced TiO2 nanotube arrays for the removal of COVID-19 aided antibiotic ciprofloxacin from water: Process implications and toxicological evaluation

The purpose of this study was to evaluate the performance of synthesized TiO₂ nanotube arrays (NTAs) for the removal of the COVID-19 aided antibiotic ciprofloxacin (CIP) and the textile dye methylene blue (MB) from model wastewater. Synthesis of TiO₂ NTAs showed that anodization potential and calcination temperatures directly influence nanotube formation. The increased anodization potential from 10 to 40 V resulted in the development of larger porous nanotubes with a diameter of 36-170 nm, while the collapse of the tubular structure was registered at the highest applied potential. Furthermore, it was found that the 500 °C calcination temperature was the most prominent for the formation of the most photocatalytically active TiO₂ NTAs, due to the optimal anatase/rutile ratio of 4.60. The degradation of both model compounds was achieved with all synthesized TiO₂ NTAs; however, the most photocatalytically active NTA sample was produced at 30 V and 500 ^°C. Compared to photocatalysis, CIP degradation was greatly enhanced by 5-25 times when ozone was introduced to the photocatalytic cell (rates 0.4-4.2 × 10^-1 min^-1 versus 0.07-0.2 × 10^-1 min^-1). This resulted in the formation of CIP degradation by-products, with different mass-to-charge ratios from [M+H]⁺ 346 to 273 m/z. Even though the CIP degradation pathway is rather complex, three main mechanisms, decarboxylation, hydroxylation reaction, and piperazine ring cleavage, were proposed and explained. Furthermore, treated samples were placed in contact with the crustaceans Daphnia magna. It was found that 100% mortality was achieved when approximately 60% of the remaining TOC was present in the samples, indicating that toxic degradation by-products were formed.

pH Switchable Water Dispersed Photocatalytic Nanoparticles

Photogeneration of Reactive Oxygen Species (ROS) finds applications in fields as different as nanomedicine, art preservation, air and water depollution and surface decontamination. Here we present photocatalytic nanoparticles (NP) that are active only at acidic pH while they do not show relevant ROS photo‐generation at neutral pH. This dual responsivity (to light and pH) is achieved by stabilizing the surface of TiO₂ NP with a specific organic shell during the synthesis and it is peculiar of the achieved core shell‐structure, as demonstrated by comparison with commercial photocatalytic TiO₂ NP. For the investigation of the photocatalytic activity, we developed two methods that allow real time detection of the process preventing any kind of artifact arising from post‐treatments and delayed analysis. The reversibility of the pH response was also demonstrated as well as the selective photo‐killing of cancer cells at acidic pH.

Adsorptive Behavior of Tartaric Acid Treated Holarrhena antidysenterica and Citrullus colocynthis Biowastes for Decolourization of Congo Red Dye from Aqueous Solutions

The aim of the present work is to eradicate Congo red (CR) dye from aqueous solutions since the dye compounds are harmful to human life and the environment leading to detrimental results. For this purpose, Holarrhena antidysenterica (HA) and Citrullus colocynthis (CC) adsorbents were used for the adsorptive removal of Congo red dye from wastewaters. The unmodified adsorbents (U-HA and U-CC) were chemically modified using tartaric acid (TA). Morphological structures were examined by FTIR and SEM. Batch adsorption studies were tested at a variety of pH, time exposure, temperatures, and adsorbent dosages. Thermodynamic parameters such as Gibbs free energy ( $∆G^{°}$ ), enthalpy ( $∆H^{°}$ ), entropy changes ( $∆S^{°}$ ), and energy of activation ( $E_{\text{a}}$ ) were also calculated. The results revealed that tartaric acid-Citrullus colocynthis (TA-CC) gave optimum conditions of time of contact (35 min), temperature conditions (40°C), pH (3), and dosage of adsorbent (1.6 g) for maximum dye removal. Tartaric acid-Holarrhena antidysenterica (TA-HA) gave equilibrium time of contact (30 min), temperature (40°C), and pH optimum (2) along with a 1.6 g dosage of adsorbent. Mechanistic understanding of adsorption isotherm provided that the Langmuir model was followed by raw and modified adsorbents. Maximum adsorption capacities $Q_{\max }$ attained were 60.61 (mg g-1), 128.21 (mg g-1), 87.71 (mg g-1), and 131.57 (mg g-1), respectively, for U-HA, TA-HA, U-CC, and TA-CC. The results of kinetic modeling displayed a high value of $R^2$ (0.99) along with minimal error (RMSE) for dye removal showing that the pseudo-second-order kinetic model has acceptable accuracy. Fourier transform infrared proposed the electrostatic, pi-pi interactions, and hydrogen bonding as dominant adsorption mechanisms at acidic pH, respectively. Rate-determining steps comprise both surface and intraparticle diffusions. Thermodynamics indicated that the dye adsorption of CR is spontaneous, exothermic, and favorable in nature. These agricultural wastes due to specific points such as low cost, availability, and high removal rates of adsorption are highly competent for the expulsion of anionic dye like CR from wastewaters.

Current Developments in the Effective Removal of Environmental Pollutants through Photocatalytic Degradation Using Nanomaterials

Photocatalysis plays a prominent role in the protection of the environment from recalcitrant pollutants by reducing hazardous wastes. Among the different methods of choice, photocatalysis mediated through nanomaterials is the most widely used and economical method for removing pollutants from wastewater. Recently, worldwide researchers focused their research on eco-friendly and sustainable environmental aspects. Wastewater contamination is one of the major threats coming from industrial processes, compared to other environmental issues. Much research is concerned with the advanced development of technology for treating wastewater discharged from various industries. Water treatment using photocatalysis is prominent because of its degradation capacity to convert pollutants into non-toxic biodegradable products. Photocatalysts are cheap, and are now emerging slowly in the research field. This review paper elaborates in detail on the metal oxides used as a nano photocatalysts in the various type of pollutant degradation. The progress of research into metal oxide nanoparticles, and their application as photocatalysts in organic pollutant degradation, were highlighted. As a final consideration, the challenges and future perspectives of photocatalysts were analyzed. The application of nano-based materials can be a new horizon in the use of photocatalysts in the near future for organic pollutant degradation.

One-pot multicomponent green LED photoinduced synthesis of chromeno[4,3-b]chromenes catalyzed by a new nanophotocatalyst histaminium tetrachlorozincate

Histaminium tetrachlorozincate nanoparticles are prepared, characterized and applied as an effective and recoverable photocatalyst in the one-pot, green and multi-component synthesis of various chromenes by the reaction of dimedone and/or 1,3-cyclohexanedione, arylaldehyde and 4-hydroxycoumarin in high yields under solventless conditions at ambient temperature. This new catalyst is characterized by FT-IR, XRD, EDX, NMR, SEM and TEM techniques. The incorporation of histaminium ions into the framework of ZnCl₄²⁻ significantly affected the photocatalytic activity of tetrachlorozincate such that good reusability and recyclability are attained. Moreover, reactive species such as ˙O₂⁻ and hydroxyl radicals have proved to be active species in the presented photocatalytic reaction. In addition, the hot filtration test confirms enough stability of the photocatalyst and no significant leaching and destruction of the framework in the course of the reaction. The major advantages of the presented methodology include easy work-up, cost effectiveness, nontoxic nature, broad substrate scope, 100% atom economy, ease of separation, and environment friendly reaction conditions. Finally, the catalyst could be reused many times without significant loss of activity.

(His.)ZnCl₄ nanocatalyst is realized for the preparation of chromenes with a green LED. ˙O₂⁻, OH˙ and h⁺ are reactive species for this reaction. Complementary tests assured good stability and reusability of the nanophotocatalyst.

Selective photocatalytic oxidation of aromatic alcohols to aldehydes with air by magnetic WO3ZnO/Fe3O4. In situ photochemical synthesis of 2-substituted benzimidazoles

Recently, visible light-driven organic photochemical synthesis has been a pioneering field of interest from academic and industrial associations due to its unique features of green and sustainable chemistry. Herein, WO3ZnO/Fe3O4 was synthesized, characterized, and used as an efficient magnetic photocatalyst in the preparation of a range of 2-substituted benzimidazoles via the condensation of benzyl alcohol and o-phenylenediamine in ethanol at room temperature for the first time. The key feature of this work is focused on the in situ photocatalytic oxidation of benzyl alcohols to benzaldehydes under atmospheric air and in the absence of any further oxidant. This new heterogeneous nanophotocatalyst was characterized via XRD, FT-IR, VSM and SEM. Short reaction time, cost-effectiveness, broad substrate scope, easy work-up by an external magnet, and excellent product yield are the major advantages of the present methodology. A number of effective experimental parameters were also fully investigated to clear broadness and generality of the protocol.

Iron Oxide/Phosphatic Materials Composites with Potential Applications in Environmental Protection

Currently, hydroxyapatite is probably the most researched material, due to its multiple applications in medical, environmental, or cultural heritage, when the classical structure is modified and calcium is displaced partially or totally with different metals. By changing the classical structure of the hydroxyapatite, new morphologies can be obtained, thus allowing final applications different from those of the initial hydroxyapatite material. However, their properties should be tuned for the desired application. In this context, the present paper describes the synthesis and characterization (through energy-dispersive X-ray fluorescence, X-ray diffraction, FTIR, thermal analysis, and transmission electron microscopy) of iron oxide/manganese-containing phosphatic phase composite materials, developed in order to obtain the enhancement of final environmental applications (photodegradation of dyes, adsorption of organic compounds). The composite material was tested for photocatalytic properties, after embedding in hydrosoluble film-forming materials. Photocatalytic coatings show different activity during the photodecomposition of Methylene Blue, used as a model of a contaminant. The photocatalytic activities of the materials were discussed in relationship with both the phosphatic materials and the magnetic components. Finally, other environmental applications were studied for the developed materials (adsorption of non-steroidal anti-inflammatory drugs—paracetamol and ibuprofen), revealing an enhancement of the adsorption capacity of the phosphatic material upon addition of the magnetic phase.

Photocatalysis for Organic Wastewater Treatment: From the Basis to Current Challenges for Society

Organic pollutants such as dyes, antibiotics, analgesics, herbicides, pesticides, and stimulants become major sources of water pollution. Several treatments such as absorptions, coagulation, filtration, and oxidations were introduced and experimentally carried out to overcome these problems. Nowadays, an advanced technique by photocatalytic degradation attracts the attention of most researchers due to its interesting and promising mechanism that allows spontaneous and non-spontaneous reactions as they utilized light energy to initiate the reaction. However, only a few numbers of photocatalysts reported were able to completely degrade organic pollutants. In the past decade, the number of preparation techniques of photocatalyst such as doping, morphology manipulation, metal loading, and coupling heterojunction were studied and tested. Thus, in this paper, we reviewed details on the fundamentals, common photocatalyst preparation for coupling heterojunction, morphological effect, and photocatalyst’s characterization techniques. The important variables such as catalyst dosage, pH, and initial concentration of sample pollution, irradiation time by light, temperature system, durability, and stability of the catalyst that potentially affect the efficiency of the process were also discussed. Overall, this paper offers an in-depth perspective of photocatalytic degradation of sample pollutions and its future direction.