Amoxicillin photodegradation under visible light catalyzed by metal-free carbon nitride: An investigation of the influence of the structural defects

Light-driven photocatalysis as an effective tool for degradation of antibiotics

Antibiotic contamination has become a severe issue and a dangerous concern to the environment because of large release of antibiotic effluent into terrestrial and aquatic ecosystems. To try and solve these issues, a plethora of research on antibiotic withdrawal has been carried out. Recently photocatalysis has received tremendous attention due to its ability to remove antibiotics from aqueous solutions in a cost-effective and environmentally friendly manner with few drawbacks compared to traditional photocatalysts. Considerable attention has been focused on developing advanced visible light-driven photocatalysts in order to address these problems. This review provides an overview of recent developments in the field of photocatalytic degradation of antibiotics, including the doping of metals and non-metals into ultraviolet light-driven photocatalysts, the formation of new semiconductor photocatalysts, the advancement of heterojunction photocatalysts, and the building of surface plasmon resonance-enhanced photocatalytic systems.

Efficient photoelectrochemical real textile wastewater detoxification using photoanodes of C3N4-BiVO4

Photoelectrochemical systems utilizing solar energy have garnered significant attention for their sustainability in remediating contaminated water. This study focuses on advancing photoanode development through the utilization of carbon nitrides (C3N4) and bismuth vanadate (BiVO4), two promising semiconductor materials renowned for their efficient electron-hole pair separation leading to enhanced photocatalytic activity. Four distinct materials were synthesized and compared: BiVO4 over C3N4, C3N4 over BiVO4, and pristine BiVO4 and C3N4. Upon electrochemical analysis, the C3N4-BiVO4 heterostructure exhibited the highest photoelectrocatalytic charge transfer constant, mobility, and lifetime of charge carriers. Capitalizing on these exceptional properties, the composite was applied to remove organic matter real effluent from the textile industry. The photoelectrodegradation of the effluent demonstrated substantial removal of Total Organic Carbon (TOC) and the generation of low toxicity degradation products, accompanied by low energy consumption. The compelling results underscore the high potential of the synthesized C3N4-BiVO4 heterostructure for industrial applications, particularly in addressing environmental challenges associated with textile industry effluents.

Aerogel for Highly Efficient Photocatalytic Degradation

Photocatalysis is one of the effective ways to degrade pollutant antibiotics. Agar is used as the adsorption module to provide abundant pore structure. Carbon dots (CDs) are selected as light energy conversion components. Graphitic carbon nitride (g-C3N4) is used as the main material of the catalyst. Agar/CDs/g-C3N4-functionalized aerogel with a unique 3D pore structure is assembled. The Agar/CDs/g-C3N4 aerogel shows the highest photocurrent density, which is 3.7 times that of agar, 2.4 times that of 3-g-C3N4 and 1.6 times that of Agar/g-C3N4 aerogel. Compared with 3-g-C3N4 and Agar/g-C3N4 aerogel, which can completely remove AMX after 75 min, Agar/CDs/g-C3N4 aerogel can degrade amoxicillin (AMX) completely after 45 min of illumination. The reason is that Agar/CDs/g-C3N4 aerogel has a larger specific surface area, richer functional groups, a wider spectral range, higher photocurrent density and better carrier migration and separation efficiency. It is a good strategy with which to combine the effects of each component in the ternary system for the efficient photocatalysis of organic pollutants.

Bio-inspired sustainable synthesis of novel SnS2/biochar nanocomposite for adsorption coupled photodegradation of amoxicillin and congo red: Effects of reaction parameters, and water matrices

This study aims to fabricate a novel integrated photocatalytic adsorbent (IPA) via a green solvothermal process employing tea (Camellia sinensis var. assamica) leaf extract as a stabilizing and capping agent for the removal of organic pollutants from wastewater. An n-type semiconductor photocatalyst, SnS_2, was chosen as a photocatalyst due to its remarkable photocatalytic activity supported over areca nut (Areca catechu) biochar for the adsorption of pollutants. The adsorption and photocatalytic properties of fabricated IPA were examined by taking amoxicillin (AM) and congo red (CR) as two emerging pollutants found in wastewater. Investigating synergistic adsorption and photocatalytic properties under varying reaction conditions mimicking actual wastewater conditions marks the novelty of the present research. The support of biochar for the SnS₂ thin films induced a reduction in charge recombination rate, which enhanced the photocatalytic activity of the material. The adsorption data were in accordance with the Langmuir nonlinear isotherm model, indicating monolayer chemosorption with the pseudo-second-order rate kinetics. The photodegradation process follows pseudo-first-order kinetics with the highest rate constant of 0.0450 min^-1 for AM and 0.0454 min^-1 for CR. The overall removal efficiency of 93.72 ± 1.19% and 98.43 ± 1.53% could be achieved within 90 min for AM and CR via simultaneous adsorption and photodegradation model. A plausible mechanism of synergistic adsorption and photodegradation of pollutants is also presented. The effect of pH, Humic acid (HA) concentration, inorganic salts and water matrices have also been included.The photodegradation activity of SnS₂ under visible light coupled with the adsorption capability of the biochar results in the excellent removal of the contaminants from the liquid phase.

Compounds based on iron mining tailing dams and activated carbon from macauba palm for removal of emerging contaminants and phosphate from aqueous systems

In this work, an iron-rich residue, which is widely obtained as a by-product in the iron mining industry, and macauba endocarp, waste from the extraction of vegetable oil for the production of biofuels, were used in the preparation of different composites based on iron and carbon. The composites were obtained by manual grinding of the calcined iron residue and activated carbon prepared by the macauba endocarp followed by thermal treatment under nitrogen atmosphere. The effect of the thermal treatment was analyzed by Mössbauer spectroscopy and X-ray diffraction and showed that the increase in the treatment temperature promoted the formation of different reduced iron phases in the final composite, such as Fe₃O₄, FeO, and Fe⁰. These composites were used in a combined adsorption/oxidation process through photocatalysis to remove up to 93% of amoxicillin from aqueous phase. The formation of possible reaction intermediates was monitored by electrospray ionization mass spectrometry (ESI-MS) and a mechanism of amoxicillin degradation was proposed. Afterward, the Fe/C composites were conducted to evaluate the impact of several parameters on phosphate adsorption processes and showed a maximum adsorption capacity of 40.3 mg g^-1. The adsorption capacity obtained for all the materials were greater than those found in the literature.

Engineering the Surface Chemistry and Morphology of Polymeric Carbon Nitrides Towards Greener Heterogeneous Catalysts for Biodiesel Synthesis

Biodiesel remains one of the most promising alternatives to replace fossil fuel-derived petrodiesel. Nonetheless, conventional biodiesel synthesis relies on homogeneous alkali-based catalysts that involve long and tedious purification steps , increasing biodiesel production costs. Heterogeneous catalysts have emerged as promising alternatives to circumvent these drawbacks, as they can easily be recovered and reused. Herein, polymeric carbon nitride dots and nanosheets are synthesized through a solid-phase reaction between urea and sodium citrate. Their morphology and surface chemistry are tuned by varying the precursor's ratio, and the materials are investigated as catalysts in the transesterification reaction of canola oil to biodiesel. A conversion of > 98% is achieved using a 5 wt% catalyst loading, oil to methanol ratio of 1:36 at 90 °C for 4 h, with the performance maintained over at least five reuse cycles. In addition, the effect of the transesterification reaction parameters on the reaction kinetics is evaluated, which follows a pseudo-first-order (PFO) regime. Combined with a deep understanding of the catalyst's surface, these results have allowed us to propose a reaction mechanism similar to the one observed for homogenous alkali catalysts. These carbon nitride-based nanoparticles offer a metal-free and cost-effective alternative to conventional homogeneous and metal-based heterogeneous catalysts.

Preparation and Characterization of a Coordination Polymer Based on Iron (III)-Cyamelurate as a Superior Catalyst for Heterogeneous Fenton-Like Processes

We report on a new iron (iii)-cyamelurate-based coordination polymer. The new material based on a heptazine derivative was prepared in aqueous medium and characterized by a variety of techniques including TGA, FTIR, XRD, HRTEM, and STEM. Due to the high structural stability of the complex in aqueous media, its heterogeneous Fenton-like catalytic activity was evaluated using a model molecule. The results obtained showed a high catalytic activity in both in basic and acid media. The pseudo-first-order rate constants normalized by iron(III) concentrations was approximately 1000 times higher than the result obtained for traditional heterogeneous catalysts based on iron(III) oxyhydroxides. The best observed catalytic activities were attributed to the increase in the binding sites of Fe³⁺ ions, in parallel with the increased exposure of the catalytic sites, leading to a higher atomic efficiency of the reaction.

Enhanced Visible-Light-Responsive Photocatalytic Degradation of Ciprofloxacin by the CuxO/Metal-Organic Framework Hybrid Nanocomposite

Ciprofloxacin (CIP) is a commonly used antibiotic, however, once in the environment, it is highly toxic with a poor biodegradability. Given these attributes, an effective strategy for the removal of CIP is urgently needed for the protection of water resources. Herein, a novel copper metal-organic framework (CuxO/MOF) multifunctional material has been produced, in this work, by the calcination of Cu-MOF urea at 300 °C, in the presence of a 5% H2 atmosphere. The morphological, structural, and thermal properties of the prepared CuxO/MOF were determined through various techniques, and its photocatalytic behavior was investigated for the degradation of CIP under visible-light irradiation. The prepared CuxO/MOF bifunctional material is presented as a graphitic carbon-layered structure with a particle size of 9.2 ± 2.1 nm. The existence of CuO-Cu2O-C, which was found on the CuxO/MOF surface, enhanced the adsorption efficiency and increased the photosensitivity of CuxO/MOF, towards the degradation of CIP in aqueous solutions. The tailored CuxO/MOF, not only shows an excellent CIP degradation efficiency of up to 92% with a constant kinetic rate (kobs) of 0.048 min−1 under visible light, but it can also retain the stable photodegradation efficiency of >85%, for at least six cycles. In addition, CuxO/MOF has an excellent adsorption capacity at pH 6.0 of the maximum Langmuir adsorption capacity of 34.5 mg g−1 for CIP. The results obtained in this study demonstrate that CuxO/MOF is a reliable integrated material and serves as an adsorbent and photocatalyst, which can open a new pathway for the preparation of visible-light-responsive photocatalysts, for the removal of antibiotics and other emerging pollutants.

A review of radical and non-radical degradation of amoxicillin by using different oxidation process systems

Pharmaceutical compounds have piqued the interest of researchers due to an increase in their demand, which increases the possibility of leakage into the environment. Amoxicillin (AMX) is a penicillin derivative used for the treatment of infections caused by gram-positive bacteria. AMX has a low metabolic rate in the human body, and around 80-90% is unmetabolized. As a result, AMX residuals should be treated immediately to avoid further accumulation in the environment. Advanced oxidation process techniques are an efficient way to degrade AMX. This review attempts to collect, organize, summarize, and analyze the most up to date research linked to the degradation of AMX by different advanced oxidation process systems including photocatalytic, ultrasonic, electro-oxidation, and advanced oxidation process-based on partials. The main topics investigated in this review are degradation mechanism, degradation efficiency, catalyst stability, the formation of AMX by-products and its toxicity, in addition, the influence of different experimental conditions was discussed such as pH, temperature, scavengers, the concentration of amoxicillin, oxidants, catalyst, and doping ratio. The degradation of AMX could be inhibited by very high values of pH, temperature, AMX concentration, oxidants concentration, catalyst concentration, and doping ratio. Several AMX by-products were discovered after oxidation treatment, and several of them had lower or same values of LC₅₀ (96 h) fathead minnow of AMX itself, such as m/z 384, 375, 349, 323, 324, 321, 318, with prediction values of 0.70, 1.10, 1.10 0.42, 0.42, 0.42, and 0.42 mg/L, respectively. We revealed that there is no silver bullet system to oxidize AMX from an aqueous medium. However, it is recommended to apply hybrid systems such as Photo-electro, Photo-Fenton, Electro-Fenton, etc. Hybrid systems are capable to cover the drawbacks of the single system. This review may provide important information, as well as future recommendations, for future researchers interested in treating AMX using various AOP systems, allowing them to improve the applicability of their systems and successfully oxidize AMX from an aqueous medium.

One-pot synthesis of Zn-CdS@C nanoarchitecture with improved photocatalytic performance toward antibiotic degradation

In this paper, carbon-coated Zn doped CdS core-shell photocatalyst (Zn-CdS@C) was fabricated via one-pot solvothermal method. The obtained Zn-CdS@C architectures displayed enhanced performance in photocatalytic antibiotic removal process. The Zn doped sites and carbon shell could all contribute to the prolonged lifetime of charge carriers and furthermore, result in the improved photoactivity. Moreover, the carbon shell could effectively improve the corrosion resistance of sulfide photocatalyst. We hope this study could provide novel insights into the fabrication of highly-efficient carbon-coated core-shell nanostructure toward wastewater treatment.

Carbon nitride-based Z-scheme heterojunctions for solar-driven advanced oxidation processes

Solar-driven advanced oxidation processes (AOPs) via direct photodegradation or indirect photocatalytic activation of typical oxidants, such as hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS), and peroxydisulfate (PDS), have been deemed to be an efficient technology for wastewater remediation. Artificial Z-scheme structured materials represent a promising class of photocatalysts due to their spatially separated charge carriers and strong redox abilities. Herein, we summarize the development of metal-free graphitic carbon nitride (g-C₃N₄, CN)-based direct and indirect Z-scheme photocatalysts for solar-driven AOPs in removing organic pollutants from water. In the work, the classification of AOPs, definition and validation of Z-schemes are summarized firstly. The innovative engineering strategies (e.g., morphology and dimensionality control, element doping, defect engineering, cocatalyst loading, and tandem Z-scheme construction) over CN-based direct Z-scheme structure are then examined. Rational design of indirect CN-based Z-scheme systems using different charge mediators, such as solid conductive materials and soluble ion pairs, is further discussed. Through examining the relationship between the Z-scheme structure and activity (charge transfer and separation, light absorption, and reaction kinetics), we aim to provide more insights into the construction strategies and structure modification on CN-based Z-schemes towards improving their catalytic performances in AOPs. Lastly, limitations, challenges, and perspectives on future development in this emerging field are proposed.

Levofloxacin degradation under visible-LED photo-catalyzing by a novel ternary Fe-ZnO/WO3 nanocomposite

As semiconductor photocatalysts showing their efficient redox ability upon illumination, new development of materials to enhance the pollution degradation is gaining popularity, especially on their oxidation ability. In this study, a highly stable ternary Fe-ZnO/WO₃ nanocomposite photocatalyst has been synthesized in order to improve charge transfer of photocatalytic oxidation under 30W LED light (425-470 nm) to efficiency degrade the Levofloxacin (LVF) in the solution. This catalyst was characterized and analyzed by XRD, FE-SEM, HR-TEM, X-ray XPS, UPS, PL, TRPL, LSV, EIS, and Photocurrent. Various important factors for the photodegradation were investigated, including Fe content, initial LVF concentration, catalyst dosage, and solution pH. The optimal conditions were Fe 1.0 wt%, LVF 10 mg L^-1, Fe-ZnO/WO₃ dosage 0.5 g L^-1, and pH 7 for LVF photodegradation up to 96% with a kinetic rate constant of 0.0342 min^-1 and were stable in photodegradation efficiency (90%) after five test cycles. In the visible LED light, the activation bandgap was estimated to be 2.75 eV with high electron-hole pair separation and charge transfer from Fe-ZnO to WO₃ that could enhance the generation of active species of ^•OH. Moreover, the more effective charge separation of Fe-ZnO/WO₃ were confirmed by lower PL intensity and longer charge carrier lifetime. Fe-ZnO/WO₃ also demonstrated the excellent electrochemical properties with high photocurrent and small resistance. For the LVF degradation, 3 possible pathways were proposed with 12 intermediate products. This study demonstrated that the synthesized Fe-ZnO/WO₃ could serve as a reliable visible-light responsive photocatalysts with the potential for degrading antibiotics in solution.

Detection of singlet oxygen by EPR: The instability of the nitroxyl radicals

The use of spin traps and redox probes coupled with electron paramagnetic resonance (EPR) is a method frequently applied in the evaluation of the efficiency of photosensitizers and photocatalysts in phototherapeutic and photocatalytic processes that involve reactive oxygen species. In this way, the method helps to clarify the mechanism behind photo-induced reactions. Hydroxy-TEMP is a very specific redox probe for selectively identifying and quantifying singlet oxygen (¹O₂). In this work, the kinetics of radical generated by the oxidation products of the Hydroxy-TEMP redox probe was analyzed from EPR spectra in aqueous solutions of several water-soluble porphyrins ([H₂T4MPyP](OTs)₄, Na₄[H₂T4SPP], [H₂T2MPyP](OTs)₄, [ZnT4MyPyP](OTs)₄, [MnT4MyPyP](OTs)₅, H₂T4CPP, and [H₂T4TriMAPP](OTs)4) under white light illumination. Different factors such as the concentration of the redox probe, pH of the medium, and photostability of the porphyrins were evaluated. A systematic study was carried out to reveal the factors associated with stable radical degradation (TEMPOL) by illumination in the visible spectral region in systems containing photosensitizer (porphyrin) and redox probe (Hydroxy-TEMP). With the aid of EPR and gas chromatography coupled with mass spectroscopy (GC-MS) techniques, the mechanism of the radical degradation and the photobleaching of porphyrins were investigated. After successive interactions with the porphyrin in its excited state, in alkaline aqueous solution (pH > 10), the free radical TEMPOL is transformed into TEMPONE until the final diamagnetic product Phorone. A protocol was elaborated to identify and quantify the generation of ¹O₂ by Hydroxy-TEMP reliably, to avoid possible errors in the interpretation of efficiency of photosensitizers.

Sheet-on-sheet TiO2/Bi2MoO6 heterostructure for enhanced photocatalytic amoxicillin degradation

Developing sheet-on-sheet (2D/2D) heterostructure with built-in electric field (BIEF) is effective in boosting the performance of photocatalysts for emerging contaminants degradation. Herein, the 2D/2D microtopography and (-)TiO₂/(+)Bi₂MoO₆ BIEF were precisely integrated into hierarchical nanosheets, which can provide the basis and driving force for charge transfer both in in-plane and interface of heterojunction. The prepared photocatalyst (TiO₂/Bi₂MoO₆) showed high-efficiency and stable performance for photocatalytic amoxicillin (AMX) degradation, which was 18.2 and 5.7 times higher than TiO₂ and Bi₂MoO₆, respectively. More importantly, TiO₂/Bi₂MoO₆ showed more efficient photocatalytic activity and photogenerated charge separation than TiO₂@Bi₂MoO₆ (different morphology). Besides, four possible pathways of AMX degradation were proposed depending on Gaussian calculations and intermediates analysis by GC-MS and HPLC-TOFMS. This work sheds light on the design and construction of unique 2D/2D heterostructure photocatalysts for AMX degradation.

Cu-doped g-C3N4 catalyst with stable Cu0 and Cu+ for enhanced amoxicillin degradation by heterogeneous electro-Fenton process at neutral pH

The development of new heterogeneous Cu-based solid catalysts for hydroxyl radical (∙OH) generation plays a crucial role in degradation of pollutants at neutral pH circumstance. In this work, a Cu-doped graphitic carbon nitride (g-C₃N₄) complex was synthesized in one-step pyrolysis process using copper chloride dihydrate and dicyandiamide as precursors. The results reveal that after Cu doping, the bulk structure of g-C₃N₄ was destroyed with fragmentary morphology formation. Besides, Cu⁰ and Cu⁺ were successfully embedded in g-C₃N₄ sheet. Moreover, amoxicillin (AMX) removal by heterogeneous electro-Fenton process was performed to evaluate the catalytic activity of the Cu-doped g-C₃N₄. 99.1% AMX removal efficiency was obtained after 60 min electrolysis under neutral pH condition when the current density was 12 mA cm² and the catalyst dosage was 0.3 g L^-1. Both Cu⁰ and Cu⁺ were stably retained in the Cu-doped g-C₃N₄ catalyst and AMX removal efficiency reached 91.1%, even after 5 cycles, manifesting the remarkable stability of Cu-doped g-C₃N₄. Also, Cu-doped g-C₃N₄ possessed excellent catalytic activities for AMX removal in various waterbodies. According to the catalytic mechanism analysis, the ∙OH was proved to be the primary reactive species for AMX removal in heterogeneous electro-Fenton process. Based on the identification of sixteen different intermediate products, the possible degradation pathways were proposed. This work provides a simple method to synthesize a Cu-based solid catalyst containing stable Cu⁰ and Cu ⁺ for degradation of pollutants in wastewater.

Degradation of amoxicillin with sono, photo, and sonophotocatalytic oxidation under low-frequency ultrasound and visible light

The presence of pharmaceutically active compounds in aquatic bodies is a global concern, and suitable treatment technologies are required. In this study, the efficacy of photocatalytic, sonocatalytic, and sonophotocatalytic oxidation processes for the degradation of amoxicillin (AMX) was investigated using visible light with N doped TiO₂ (N-TiO₂) nanoparticles as the catalyst and low-frequency ultrasound in a novel multifrequency reactor. The influence of different operational parameters on the extent of AMX degradation was studied. Sonophotocatalytic oxidation was found more efficient for AMX degradation when compared to photocatalysis or sonocatalysis alone, and may be due to the reduced bandgap of the catalyst, enhanced cavitation effect due to the presence of the solid catalyst, and improved mass transfer of pollutants. AMX degradation during sono, photo, and sonophotocatalytic oxidation processes was in good agreement with pseudo-first-order kinetics. Empirical kinetic models were also developed using multiple linear regression for predicting the degradation efficiency accounting for the operational parameters. Scavenger experiments suggested that ^•OH radicals largely contributed to AMX degradation, and a plausible mechanism for degradation was proposed. Further, possible degradation pathways for all three treatment processes are also proposed after identifying the degradation products.