In Situ Synthesis of Doped Bio-Graphenes as Effective Metal-Free Catalysts in Removal of Antibiotics: Effect of Natural Precursor on Doping, Morphology, and Catalytic Activity

Wastewater contaminated with antibiotics is a major environmental challenge. The oxidation process is one of the most common and effective ways to remove these pollutants. The use of metal-free, green, and inexpensive catalysts can be a good alternative to metal-containing photocatalysts in environmental applications. We developed here the green synthesis of bio-graphenes by using natural precursors (Xanthan, Chitosan, Boswellia, Tragacanth). The use of these precursors can act as templates to create 3D doped graphene structures with special morphology. Also, this method is a simple method for in situ synthesis of doped graphenes. The elements present in the natural biopolymers (N) and other elements in the natural composition (P, S) are easily placed in the graphene structure and improve the catalytic activity due to the structural defects, surface charges, increased electron transfers, and high absorption. The results have shown that the hollow cubic Chitosan-derived graphene has shown the best performance due to the doping of N, S, and P. The Boswellia-derived graphene shows the highest surface area but a lower catalytic performance, which indicates the more effective role of doping in the catalytic activity. In this mechanism, O2 dissolved in water absorbs onto the positively charged C adjacent to N dopants to create oxygenated radicals, which enables the degradation of antibiotic molecules. Light irradiation increases the amount of radicals and rate of antibiotic removal.

Photodegradation of fleroxacin by g-C3N4/PPy/Ag and HPLC-MS/MS analysis of degradation pathways

To improve the photocatalytic activity of g-C₃N₄, graphitic phase carbon nitride was prepared using melamine as the substrate and modified with PPy and Ag nanoparticles. The structure, morphology, and optical properties of the photocatalysts were investigated using various characterization methods such as XRD, FT-IR, TEM, XPS, and UV-vis DRS. The degradation of fleroxacin, a common quinolone antibiotic, was isolated and measured using the HPLC-MS/MS technique to trace its intermediates and deduce the main degradation pathways. The results showed that g-C₃N₄/PPy/Ag had high photocatalytic activity and a degradation rate of more than 90%. The fleroxacin degradation reactions were primarily oxidative ring opening of the N-methyl piperazine ring structure, defluorination reactions on fluoroethyl, HCHO, and N-methyl ethylamine removal reactions.

Preparation of Fluorescent Carbon Dots Composites and Their Potential Applications in Biomedicine and Drug Delivery-A Review

Carbon dots (CDs), a new member of carbon nanostructures, rely on surface modification and functionalization for their good fluorescence phosphorescence and excellent physical and chemical properties, including small size (<10 nm), high chemical stability, biocompatibility, non-toxicity, low cost, and easy synthesis. In the field of medical research on cancer (IARC), CDs, a new material with unique optical properties as a photosensitizer, are being applied to heating local apoptosis induction of cancer cells. In addition, imaging tools can also be combined with a drug to form the nanometer complex compound, the imaging guidance for multi-function dosage, so as to improve the efficiency of drug delivery, which also plays a big role in genetic diagnosis. This paper mainly includes three parts: The first part briefly introduces the synthesis and preparation of carbon dots, and summarizes the advantages and disadvantages of different preparation methods; The second part introduces the preparation methods of carbon dot composites. Finally, the application status of carbon dot composites in biomedicine, cancer theranostics, drug delivery, electrochemistry, and photocatalysis is summarized.

Rice Husk-Derived Carbon Quantum Dots-Based Dual-Mode Nanoprobe for Selective and Sensitive Detection of Fe3+ and Fluoroquinolones

Herein, eco-friendly, water-soluble, and fluorescent carbon quantum dots (CQDs) with an average size of 8.3 nm were synthesized from rice husk (RH) using the hydrothermal method, and the CQDs were labeled as rice husk CQDs (RH-CQDs). The composition and surface functionalities were studied using X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. A study on the impact of pH and irradiation time on fluorescence affirmed the stability of RH-CQDs. The as-synthesized nanosensor has high selectivity and sensitivity for Fe³⁺ ions. Several photophysical studies were performed to investigate the interaction between RH-CQDs and Fe³⁺. Using the time-correlated single-photon technique, it is determined that the average lifetime value of RH-CQDs significantly decreases in the presence of Fe³⁺, which supports a dynamic quenching mechanism. The developed sensor exhibited excellent sensitivity with a detection limit in the nanomolar range (149 nM) with a wide linear range of 0-1300 nM for Fe³⁺ ions. The prepared nanosensor was also used to detect Fe³⁺ in a tablet supplement with high recoveries. Moreover, the RH-CQD nanoprobe was used to detect other analytes (fluoroquinolones) using the fluorescence enhancement technique. It showed high selectivity and sensitivity toward ofloxacin (OFX) and ciprofloxacin (CPX). The detection limits calculated were 150 nM and 127 nM with a linearity range of 50-1150 nM for OFX and CPX, respectively. The enhancement of the average lifetime value and quantum yield in the presence of OFX and CPX favors the increased fluorescence property of RH-CQDs through hydrogen bonding and charge transfer. In this work, the integration of two different mechanisms (fluorescence quenching and fluorescence enhancement) was followed to construct a single sensing platform for accurate quantification of dual-mode nanosensors for the detection of metal ions and fluoroquinolones by the excited-state electron transfer and hydrogen bonding mechanism, respectively. This strategy also stimulates the detection of more than one analyte.

Current advances on the photocatalytic degradation of fluoroquinolones: photoreaction mechanism and environmental application

Heterogeneous photocatalysis is one of the most studied and promising techniques for degradation of contaminants of emerging concern, especially pharmaceuticals, and it represents a potential application in wastewater treatment of recalcitrant pollutants, such as fluoroquinolones, which are almost not abated by standard WWTPs. Although photodegradation partially contributes to alleviate their accumulation into the aquatic systems, heterogeneous photocatalysis assures complete sequestration and mineralization of FQs and their photoproducts and offers many advantages with respect to the other advanced oxidation processes (AOPs). The present brief review summarizes the most recent studies regarding the development and application of novel photocatalytic materials to the removal of FQs from contaminated waters. The collected data are arranged relating the mechanistic aspects to specific catalysts' properties, such as adsorption capacity, easy recovery, and reusability, especially under actual conditions.

Efficient Combination of G-C3 N4 and CDs for Enhanced Photocatalytic Performance: A Review of Synthesis, Strategies, and Applications

Recently, heterogeneous photocatalysts have achieved much interest on account of their great potential applications in resolving many tough energy and environmental troubles around the world through an ecologically sustainable way. Heterogeneous nanocomposites composed of graphitic carbon nitride (g-C₃ N₄ ) and carbon dots (CDs) possess broad spectrum absorption, appropriate electronic band structures, rapid carrier mobility, abundant reserves, excellent chemical stability, and facile synthesis methods, which make them promising composite photocatalysts for suitable applications such as photocatalytic solar fuels production and contaminant decomposition. With the rapid development in photocatalysis by hybridization of g-C₃ N₄ and CDs, a systematic summary and prospection of performance improvement are urgent and meaningful. This review first focuses on various kinds of effectively synthetic methods of composites. Following, the strategies available for enhanced performance, including morphology optimization, spectral absorption improvement, ternary or quaternary composition hybrid, lateral or vertical heterostructures construction, heteroatom doping, and so forth, are fully discussed. Then, the applications mainly in efficient photocatalytic hydrogen generation, photocatalytic carbon dioxide reduction, and organic pollutants degradation are systematically demonstrated. Finally, the remaining issues and prospect of further development are proposed as some kind of guidance for powerful combination of g-C₃ N₄ and CDs with high efficiency to photocatalysis.

Efficient and effective removal of emerging contaminants through the parallel coupling of rapid adsorption and photocatalytic degradation: A case study of fluoroquinolones

The development of efficient, effective, and large-scale treatment methods to address high-risk emerging contaminants (ECs) is a growing challenge in environmental remediation. Herein, a novel parallel coupling strategy of adsorption separation and photodegradation regeneration (parallel ASPR) is proposed; subsequently, an adsorptive photocatalyst (Zn-doped BiOI) is designed to demonstrate how to effectively eliminate fluoroquinolones (FQs) from water with the proposed ASPR scheme. Compared with pure BiOI, the addition of Zn²⁺ during synthesis has a significant influence on the morphology and structure of the products, resulting in Zn-doped BiOI samples with up to 5 times the specific surface area, 32 times the adsorption capacity, and 20 times the photocurrent intensity. The optimized Zn-doped BiOI sample has an excellent adsorption efficiency for FQs with a removal rate that exceeds 95% after 5 min of adsorption for all 6 tested FQ antibiotics. Then the adsorbed contaminants can be effectively degraded during the later visible-light irradiation process, and the adsorbent can be regenerated synchronously, showing excellent ASPR cycling performances. The mechanisms of rapid adsorption and photocatalysis were explored via material characterizations, adsorption models, density functional theory calculations, and photogenerated species analyses. The results reveal that the enhanced adsorption of Zn-doped BiOI for FQs is due to its high specific surface area, coordination-based chemical adsorption, and surface electrostatic attraction, while its superior visible-light photodegradation performance is mainly ascribed to its strong redox ability, abundant surface oxygen vacancies, and enhanced photogenerated carrier separation efficiency.

Applications of electron spin resonance spectroscopy in photoinduced nanomaterial charge separation and reactive oxygen species generation

Nano-metals, nano-metal oxides, and carbon-based nanomaterials exhibit superior solar-to-chemical/photo-electron transfer properties and are potential candidates for environmental remediations and energy transfer. Recent research effort focuses on enhancing the efficiency of photoinduced electron-hole separation to improve energy transfer in catalytic reactions. Electron spin resonance (ESR) spectroscopy has been used to monitor the generation of electron/hole and reactive oxygen species (ROS) during nanomaterial-mediated photocatalysis. Using ESR coupled with spin trapping and spin labeling techniques, the underlying photocatalytic mechanism involved in the nanomaterial-mediated photocatalysis was investigated. In this review, we briefly introduced ESR principle and summarized recent advancements using ESR spectroscopy to characterize electron-hole separation and ROS production by different types of nanomaterials.

Comparison of Graphitic Carbon Nitrides Synthetized from Melamine and Melamine-Cyanurate Complex: Characterization and Photocatalytic Decomposition of Ofloxacin and Ampicillin

Graphitic carbon nitride (g-C₃N₄, hereafter abbreviated as CN) was prepared by the heating of melamine (CN-M) and melamine-cyanurate complex (CN-MCA), respectively, in air at 550 °C for 4 h. The specific surface area (SSA) of CN-M and CN-MCA was 12 m² g⁻¹ and 225 m²g⁻¹ and the content of oxygen was 0.62 wt.% and 1.88 wt.%, respectively. The band gap energy (E_g) of CN-M was 2.64 eV and E_g of CN-MCA was 2.73 eV. The photocatalytic activity of the CN materials was tested by means of the decomposition of antibiotics ofloxacin and ampicillin under LED irradiation of 420 nm. The activity of CN-MCA was higher due to its high SSA, which was determined based on the physisorption of nitrogen. Ofloxacin was decomposed more efficiently than ampicillin in the presence of both photocatalysts.

Review on the Visible Light Photocatalysis for the Decomposition of Ciprofloxacin, Norfloxacin, Tetracyclines, and Sulfonamides Antibiotics in Wastewater

Antibiotics are chemical compounds that are used to kill or prevent bacterial growth. They are used in different fields, such as the medical field, agriculture, and veterinary. Antibiotics end up in wastewater, which causes the threat of developing antibacterial resistance; therefore, antibiotics must be eliminated from wastewater. Different conventional elimination methods are limited due to their high cost and effort, or incomplete elimination. Semiconductor-assisted photocatalysis arises as an effective elimination method for different organic wastes including antibiotics. A variety of semiconducting materials were tested to eliminate antibiotics from wastewater; nevertheless, research is still ongoing due to some limitations. This review summarizes the recent studies regarding semiconducting material modifications for antibiotic degradation using visible light irradiation.

Synthesis of a carbon dots modified g-C3N4/SnO2 Z-scheme photocatalyst with superior photocatalytic activity for PPCPs degradation under visible light irradiation

As an emerging carbon nanomaterial, carbon dots (CDs) have superior prospects for applications in the area of photocatalysis due to their unique optical and electronic properties. In this study, a novel CDs modified g-C₃N₄/SnO₂ photocatalyst (CDs/g-C₃N₄/ SnO₂) was successfully synthesized by the thermal polymerization. Under visible light irradiation, the resulting CDs/g-C₃N₄/SnO₂ photocatalyst exhibited excellent photocatalytic activity for the degradation of indomethacin (IDM). It was demonstrated that a 0.5 % loading content of CDs led to the highest IDM degradation rate, which was 5.62 times higher than that of pristine g-C₃N₄. This improved photocatalytic activity might have been attributed to the unique up-conversion photoluminescence (PL) properties and efficient charge separation capacities of the CDs. Moreover, the combination of g-C₃N₄ with SnO₂ improved the separation of photoinduced carriers and augmented the specific surface area. Reactive species (RSs) scavenging experiments and electron spin resonance (ESR) revealed that superoxide radical anions (O₂^·-) and photogenerated holes (h⁺) played critical roles during the photocatalytic process. The results of the detection of H₂O₂ and ESR confirmed that CDs/g-C₃N₄/ SnO₂ was a Z-scheme heterojunction photocatalyst. Further, HRAM LC-MS/MS was employed to identify the byproducts of IDM, and the major IDM degradation pathways of the CDs/g-C₃N₄/SnO₂ photocatalyst were proposed. This study provides new ideas for the design of novel CDs modified photocatalysts for environmental remediation.

Conventional and emerging technologies for removal of antibiotics from wastewater

Antibiotics and pharmaceuticals related products are used to enhance public health and quality of life. The wastewater that is produced from pharmaceutical industries still contains noticeable amount of antibiotics, and this has remained one of the major environmental problems facing public health. The conventional wastewater remediation approach employed by the pharmaceutical industries for the antibiotics wastewater removal is unable to remove the antibiotics completely. Besides, municipal and livestock wastewater also contain unmetabolized antibiotics released by human and animal, respectively. The antibiotic found in wastewater leads to antibiotic resistance challenges, also emergence of superbugs. Currently, numerous technological approaches have been developed to remove antibiotics from the wastewater. Therefore, it was imperative to critically review the weakness and strength of these current advanced technological approaches in use. Besides, the conventional methods for removal of antibiotics such as Klavaroti et al., Homem and Santos also discussed. Although, membrane treatment is discovered as the ultimate choice of approach, to completely remove the antibiotics, while the filtered antibiotics are still retained on the membrane. This study found, hybrid processes to be the best solution antibiotics removal from wastewater. Nevertheless, real-time monitoring system is also recommended to ascertain that, wastewater is cleared of antibiotics.

Highly active metal-free carbon dots/g-C3N4 hollow porous nanospheres for solar-light-driven PPCPs remediation: Mechanism insights, kinetics and effects of natural water matrices

Pharmaceuticals and personal care products (PPCPs) are increasingly being scrutinized by the scientific community due to their environmental persistence. Therefore, the development of novel environmentally compatible and energy-efficient technologies for their removal is highly anticipated. In this work, a novel metal-free photocatalytic nanoreactor was successfully synthesized by anchoring carbon dots to hollow carbon nitride nanospheres (HCNS/CDs). The unique structure of these hollow nanospherical HCNS/CDs hybrids endowed them with a high population of reactive sites, while enhancing optical absorption due to internal light reflection. Simultaneously, the CDs served as "artificial antennas" to absorb and convert photons with low energy, due to their superior up-converting properties. Consequently, the HCNS/CDs demonstrated excellent photodegradation activities for the degradation of PPCPs under broad-spectrum irradiation. Remarkedly, 10 mg/L of naproxen (NPX) was completely degraded following 5 min of natural solar irradiation. It was further revealed that the O₂^•- played a significant role during the photocatalytic process, which could lead to the decomposition of NPX. The effects of natural water matrices and the degradation of trace PPCPs further supported that this photocatalytic system may be efficaciously applied for the remediation of PPCPs contamination in ambient waterways.

One-step synthesis of phosphorus/oxygen co-doped g-C3N4/anatase TiO2 Z-scheme photocatalyst for significantly enhanced visible-light photocatalysis degradation of enrofloxacin

Anatase TiO₂ nanoparticles coated with P and O co-doped g-C₃N₄ were prepared via a single-step procedure. The resulting POCN/anatase TiO₂ demonstrated remarkable performance in the degradation of enrofloxacin (ENFX). The photocatalytic activity of this heterojunction was 28.9 and 3.71 times better than that of the CN and anatase TiO₂, respectively. The microtopography of the POCN/anatase TiO₂ was revealed in this study. Co-doping with P and O increased the visible light adsorption capacity of the g-C₃N₄, whereas the anatase TiO₂ nanoparticles enhanced the adsorption properties of the ENFX and the separation of the photoinduced carriers of the POCN/anatase TiO₂. The O₂^·- and h⁺ were the main reactive oxidative species in the photocatalytic degradation of ENFX. The results of the detection of H₂O₂ and ESR confirmed that POCN/anatase TiO₂ was a type Z-scheme photocatalyst. Finally, the ENFX degradation pathways were estimated through the detection of by-products.

Nitrogen-doped carbon quantum dots-decorated 2D graphitic carbon nitride as a promising photocatalyst for environmental remediation: A study on the importance of hybridization approach

Growing concerns of water pollution by dye pollutants from the textile industry has led to vast research interest to find green solutions to address this issue. In recent years, heterogeneous photocatalysis has harvested tremendous attention from researchers due to its powerful potential applications in tackling many important energy and environmental challenges at a global level. To fully utilise the broad spectrum of solar energy has been a common aim in the photocatalyst industry. This study focuses on the development of an efficient, highly thermal and chemical stable, environmentally friendly and metal-free graphitic carbon nitride (g-C₃N₄) to overcome the problem of fast charge recombination which hinders photocatalytic performances. Nitrogen-doped carbon quantum dots (NCQDs) known for its high electronic and optical functionality properties is believed to achieve photocatalytic enhancement by efficient charge separation through forming heterogeneous interfaces. Hence, the current work focuses on the hybridisation of NCQDs and g-C₃N₄ to produce a composite photocatalyst for methylene blue (MB) degradation under LED light irradiation. The optimal hybridisation method and the mass loading required for maximum attainable MB degradation were systematically investigated. The optimum photocatalyst, 1 wt% NCQD/g-C₃N₄ composite was shown to exhibit a 2.6-fold increase in photocatalytic activity over bare g-C₃N₄. Moreover, the optimum sample displayed excellent stability and durability after three consecutive degradation cycles, retaining 91.2% of its original efficiency. Scavenging tests were also performed where reactive species, photon-hole (h⁺) was identified as the primary active species initiating the pollutant degradation mechanism. The findings of this study successfully shed light on the hybridisation methods of NCQDs which improve existing g-C₃N₄ photocatalyst systems for environmental remediation by utilising solar energy.

In situ assembly of CQDs/Bi2WO6 for highly efficient photocatalytic degradation of VOCs under visible light

A facile strategy of the assembly of CQD/Bi₂WO₆ hybrid materials, which exhibit highly efficient photocatalytic degradation of pollutants under visible light.

Carbon nitride nanoplatelet photocatalysts heterostructured with B-doped carbon nanodots for enhanced photodegradation of organic pollutants

Decorating electron-accepting materials on carbon nitride (C₃N₄) is a promising strategy to construct heterostructure catalysts for improved photocatalytic abilities. In this study, B-doped carbon-dots (B-C-dots) decorated C₃N₄ (C₃N₄/B-C-dots) catalysts were fabricated through the surface deposition. The benefits from integration of B-C-dots and C₃N₄ are four folds: (i) increasing surface area; (ii) improving visible light absorption; (iii) promoting the transfer of photoinduced carriers; and (iv) reducing the recombination of photoinduced carriers. The optimum photocatalytic activity of B-C-dots/C₃N₄ for Rhodamine B (Rh B) (or tetracycline hydrochloride (TC)) degradation was about 7.21 (6.56) and 4.80 (4.35) times higher than that of C₃N₄ and C-dots/C₃N₄, respectively, exhibiting both remarkable stability and repeatability. Moreover, enhanced photocatalytic activity of C₃N₄/B-C-dots could also be attributed to the type-II heterojunction formed between C₃N₄ and B-C-dots caused by B doping.

Fate of antibiotics in three distinct sludge treatment wetlands under different operating conditions

Sludge treatment wetlands (STWs) have recently been used to treat surplus sludge. However, the distribution of antibiotics involved in the process has not been comprehensively investigated. This study aimed to evaluate the fate of two antibiotics, i.e., ciprofloxacin (CIP) and azithromycin (AZM) in STWs during the treatment of surplus sludge. Three pilot-scale STWs units-S1 with aeration tubes, S2 with aeration tubes and reed planting, and S3 with reed planting-were constructed and operated under feeding followed by resting periods. The results showed that antibiotic content in residual sludge decreased over time and unit S2 performed the best in terms of antibiotic removal. Planting reed considerably improved the antibiotic removal performance of the STWs. Biodegradation and absorption resulted in removal of most of the antibiotics in the test units. Less than 2% of the antibiotics was taken up by plants, whereas <5% of the influent antibiotics left the STW units through the drainage discharge. Overall, STW units contributed to effectively decrease CIP and AZM to 41-72% and 49-84%, respectively.

Highly photoluminescent and temperature-sensitive P, N, B-co-doped carbon quantum dots and their highly sensitive recognition for curcumin

Temperature-sensitive P, N, B-co-doped carbon quantum dots (PNBCDs) synthesized using one-pot method exhibit many excellent features, such as strong fluorescence, good stability and sensitive detection for curcumin.

Tuning the visible-light photocatalytic degradation activity of thin nanosheets constructed porous g-C3N4 microspheres by decorating ionic liquid modified carbon dots: roles of heterojunctions and surface charges

The visible-light photocatalytic degradation activity of thin nanosheets constructed g-C₃N₄ microspheres was tuned by decorating ionic liquid modified carbon dots.

Drastically enhanced visible light-driven H2 evolution by anchoring TiO2 nanoparticles on molecularly grafted carbon nitride nanosheets via a multiple modification strategy

The development of graphitic carbon nitride (CN) based photocatalysts towards efficient visible light-driven H2 evolution is highly desired for solar energy conversion. It is well-known that bulk CN materials possess three intrinsic problems, namely, high charge recombination loss, low specific surface area, and limited sunlight harvesting range. To simultaneously overcome the abovementioned drawbacks of CN, we report an innovative multiple modification strategy, involving molecular grafting of the CN network, exfoliation to ultrathin nanosheets, and hybridization with TiO2 photocatalysts. The visible light utilization ability, specific surface area, and charge separation efficiency of the CN materials improved accordingly. As expected, the TiO2/CNX-NS heterojunction photocatalyst exhibited remarkably enhanced visible light-driven H2 production rate of 138.4 μmol h-1, which was about 4.6 times higher than that of pristine CN. The excellent photocatalytic performance under visible light confirmed the successful improvement in the corresponding drawbacks of CN by each modification. In this study, we propose the possibility of combining multiple modifications in the same system to synthesize an excellent visible light-driven photocatalyst for solar-to-fuel conversion.

The facile synthesis of a single atom-dispersed silver-modified ultrathin g-C3N4 hybrid for the enhanced visible-light photocatalytic degradation of sulfamethazine with peroxymonosulfate

A single-atom dispersed Ag loaded ultrathin g-C₃N₄ hybrid was prepared and used as a visible light-driven photocatalyst for SMT degradation in the presence of PMS.