Effect of pH on the adsorption and photocatalytic degradation of sulfadimidine in Vis/g-C3N4 progress

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.

An insight into the role of experimental parameters in advanced oxidation process applied for pharmaceutical degradation

The advanced oxidation process (AOP) is an efficient method to treat recalcitrance pollutants such as pharmaceutical compounds. The essential physicochemical factors in AOP experiments significantly influence the efficiency, speed, cost, and safety of byproducts of the treatment process. In this review, we collected recent articles that investigated the elimination of pharmaceutical compounds by various AOP systems in a water medium, and then we provide an overview of AOP systems, the formation mechanisms of active radicals or reactive oxygen species (ROS), and their detection methods. Then, we discussed the role of the main physicochemical parameters (pH, chemical interference, temperature, catalyst, pollutant concentration, and oxidant concentration) in a critical way. We gained insight into the most frequent scenarios for the proper and improper physicochemical parameters for the degradation of pharmaceutical compounds. Also, we mentioned the main factors that restrict the application of AOP systems in a commercial way. We demonstrated that a proper adjustment of AOP experimental parameters resulted in promoting the treatment performance, decreasing the treatment cost and the treatment operation time, increasing the safeness of the system products, and improving the reaction stoichiometric efficiency. The outcomes of this review will be beneficial for future AOP applicants to improve the pharmaceutical compound treatment by providing a deeper understanding of the role of the parameters. In addition, the proper application of physicochemical parameters in AOP systems acts to track the sustainable development goals (SDGs).

Inhibition mechanisms of biochar-derived dissolved organic matter to triclosan photodegradation: A remarkable role of aliphatics

Endocrine disrupting chemicals like triclosan (TCS) have been thought to be an emergent environmental pollutant. The ubiquitous dissolved organic matter (DOM) is able to interrelate with TCS and hamper its phototransformation. However, how the components in DOM can inhibit the photodegradation of DOM/TCS complex is largely unknown. Herein, we discovered that TCS photodegradation with biochar-derived DOM (BDOM) was interfered by both binding affinity and reactive oxygen species (ROS) productivity. BDOM can not only stimulate TCS photodegradation by producing ROS, but also inhibit the removal of TCS through the interactions between BDOMs and TCS. The quantification of BDOM's impact on TCS photodegradation revealed that BDOM hampered TCS removal with the proportion of -7.95 to -11.24% at pH 8.5, but strengthened it to 13.20% at pH 7.0. Binding process was more easily to inhibit TCS photodegradation in molecular form, while anionic TCS photodegradation was dominated by ROS productivity. Different inhibition mechanisms were involved in TCS photodegradation depending on the components of BDOMs. The hydroxyls and aromatic carbonyls might have hindered the attack of ROS on the phenolic hydroxyl of TCS via hydrogen bond interaction or π-π electron donor-acceptor interaction. Through hydrophobic interaction, the mobile aliphatics could greatly shield TCS to prevent ROS attack by wrapping or twining TCS, playing a significant role in inhibiting TCS removal. Results from this present study can afford a new viewpoint in elucidating the function of BDOMs in the phototransformation of organics and decrease the spread of antibiotic resistance genes.

Photodegradation of clindamycin by the dissolved black carbon is simultaneously regulated by ROS generation and the binding effect

As an essential source of the natural dissolved organic matter (DOM), dissolved black carbon (DBC) plays a vital role in the photodegradation of organics; however, there is rare information about the DBC-induced photodegradation mechanism of clindamycin (CLM), one of the widely used antibiotics. Herein, we discovered DBC-generated reactive oxygen species (ROS) stimulated CLM photodegradation. Hydroxy radical (•OH) could directly attack CLM by OH-addition reaction, the singlet oxygen (¹O₂) and superoxide (O₂^•-) contributed to the CLM degradation by transforming to •OH. In addition, the binding between CLM and DBCs inhibited the photodegradation of CLM by decreasing the concentration of freely dissolved CLM. Binding process inhibited CLM photodegradation by 0.25-1.98% at pH 7.0 and 6.1-41.77% at pH 8.5. These findings suggest that the photodegradation of CLM by DBC is simultaneously regulated by the ROS production and binding effect between CLM and DBC, benefiting the exact evaluation of the environmental impact of DBCs.

FeC2O4•2H2O enables sustainable conversion of hydrogen peroxide to hydroxyl radical for promoted mineralization and detoxification of sulfadimidine

Safe treatment of antibiotics requires efficient removal of both antibiotics and their degraded intermediates. In this study, we demonstrate that FeC₂O₄•2H₂O enables the more sustainable conversion of H₂O₂ to ^•OH than commonly used FeSO₄•7H₂O, promoting the detoxification of a typical antibiotic sulfadimidine. It was found that the FeC₂O₄/H₂O₂ system could completely degrade 250 mg L^-1 of sulfadimidine within 40 min at pH 3.0, along with decreasing the contents of chemical oxygen demand and total organic carbon by 295.0 and 33.5 mg L^-1, respectively, more efficient than those in a classical Fenton system (FeSO₄/H₂O₂). Analysis of sulfadimidine degraded intermediates and toxicity evaluation suggested that the FeC₂O₄/H₂O₂ treatment could more effectively decrease the overall toxicity of the sulfadimidine solution than the FeSO₄/H₂O₂ counterpart. The sustainability of FeC₂O₄•2H₂O in H₂O₂ conversion to ^•OH was attributed to its controlled release of Fe²⁺ into the solution to prevent the quenching of ^•OH by excessive Fe²⁺, as well as the simultaneous release of C₂O₄^2- to complex with Fe²⁺ and Fe³⁺, which could inhibit iron sludge formation and accelerate Fe³⁺/Fe²⁺ redox cycle. This study provides a promising Fenton system for the safe treatment of antibiotics and sheds light on the potential of FeC₂O₄•2H₂O in environmental remediation.

gCN-P: a coupled g-C3N4/persulfate system for photocatalytic degradation of organic pollutants under simulated sunlight

A coupled g-C3N4/PDS system, named gCN-P, has been put forward to degrade refractory organic pollutants under simulated sunlight which integrates photocatalysis and PS-AOPs (advanced oxidation of persulfate based on sulfate radicals). The coupled g-C3N4 and PDS showed superior synergistic effect for MO degradation under simulated sunlight. Results showed that almost all MO was removed in the gCN-P system after irradiation for 80 min under simulated sunlight. The degradation rate of gCN-P system was improved by 12.6 and 4.9 times compared to single PDS and g-C3N4 systems, respectively. And only by adding 0.01 g of persulfate into the gCN-P system. The results of quenching experiments and EPR showed that O2-, 1O2 and h+ were main active species for the degradation of MO in the gCN-P system under simulated sunlight. Application of the gCN-P system in tap water samples demonstrated its excellent performance in real-world water environment, and the gCN-P system was employed for removing other new contaminants such as bisphenol A, ciprofloxacin, and paracetamol. The results demonstrated the gCN-P system can effectively remove organic pollutants under sunlight in practices.

Persulfate-enhanced degradation of ciprofloxacin with SiC/g-C3N4 photocatalyst under visible light irradiation

SiC/g-C₃N₄ composite (SCN) showed the potential for photocatalytic degradation of synthetic dyes, it is deserved to study whether it is effective for the photocatalytic degradation of ciprofloxacin (CIP). In this work, persulfate-enhanced CIP degradation was investigated with SCN under visible light irradiation. The results showed that the degradation efficiency of 10 mg L^-1 CIP could reach 95% for 30 min under the conditions of 0.4 g L^-1 SCN, 2 mM persulfate (PS) and solution initial pH 6. The degradation process abided by pseudo first-order kinetic equation, and the observed rate constant (k_obs) with SCN/PS (0.132 min^-1) was 13 times of that with SCN (0.0102 min^-1), and twice of that with g-C₃N₄/PS (0.0649 min^-1). The quenching experiments and electron paramagnetic resonance analysis indicated that O₂^-· and ¹O₂ played the main role and other active species (e.g., h⁺, SO₄^-· and ·OH) also participated in CIP degradation. The possible degradation pathways were proposed through identifying the intermediate products, and the main reactions may include the ring opening of piperazine, decarbonylation, decarboxylation and defluorination. Bacterial toxicity test showed that the toxicity of the reaction solution decreased dramatically after 30 min degradation. Overall, this work could provide an efficient and environmentally friendly technology for eliminating CIP.

Efficient photocatalytic destruction of recalcitrant micropollutants using graphitic carbon nitride under simulated sunlight irradiation

The ubiquity of micropollutants (MPs) in aquatic environments has attracted increasing concern for public health and ecological security. Compared to conventional biological treatment, photocatalytic processes show more efficiency in degrading MPs, but they require expensive materials and complicated synthesis processes. This study developed an economic photocatalytic process to degrade micropollutants. We synthesized urea-based graphitic carbon nitride (g-C3N4) by a facile one-step pyrolysis method and evaluated the photocatalytic efficiency of carbamazepine (CBZ). Under simulated solar irradiation, g-C3N4 could achieve 100% removal efficiency of 0.1 mg/L CBZ in spiked wastewater effluent within 15 min, and 86.5% removal efficiency in wastewater influent after 20 min of irradiation. The porous structure of g-C3N4 promoted effective charge separation and mass transport of CBZ near the catalyst surface, enabling a high kinetic rate (0.3662 min -1). Reactive oxygen species trapping experiments revealed that superoxide radicals (O2 •-) and holes (h+) were the major active radicals. Electron paramagnetic resonance (EPR) further confirmed the presence of O2 •-, • OH, 1O2 and holes. The pH, light intensity and initial CBZ concentration were found to have significant impacts on the removal efficiency of CBZ. Possible reaction intermediates were identified and the degradation pathway was proposed. Multiple MPs were selected to further demonstrate photocatalytic efficiency of g-C3N4. The facile synthesis, superior efficiency, and versatility of g-C3N4 make it a promising catalyst for application in tertiary wastewater treatment processes.

Heavy metals, antibiotics and nutrients affect the bacterial community and resistance genes in chicken manure composting and fertilized soil

Succession of bacterial communities involved in the composting process of chicken manure, including first composting (FC), second composting (SC) and fertilizer product (Pd) and fertilized soil (FS), and their associations with nutrients, heavy metals, antibiotics and antibiotic resistance genes (ARGs) were investigated. Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant phyla observed during composting. Overall, potential pathogenic bacteria decreased from 37.18% (FC) to 3.43% (Pd) and potential probiotic taxa increased from 5.77% (FC) to 7.12% (Pd). Concentrations of heavy metals increased after second composting (SC), however, no significant differences were observed between FS and CS groups. Alpha diversities of bacterial communities showed significant correlation with heavy metals and nutrients. All investigated antibiotics decreased significantly after the composting process. The certain antibiotics, heavy metals, or nutrients was significantly positive correlated with the abundance of ARGs, highlighting that they can directly or indirectly influence persistence of ARGs. Overall, results indicated that the composting process is effective for reducing potential pathogenic bacteria, antibiotics and ARGs. The application of compost lead to a decrease in pathogens and ARGs, as well as an increase in potentially beneficial taxa and nutrients in soil.

H-bonding effect of oxyanions enhanced photocatalytic degradation of sulfonamides by g-C3N4 in aqueous solution

In this study, the effect of oxyanions on the photodegradation of sulfonamides by graphitic carbon nitride (g-C₃N₄) was investigated. The results showed that the presence of disilicate (DS) could substantially improve the photodegradation of sulfamethazine (SMZ) in g-C₃N₄ aqueous suspension. The primary mechanism for the enhancing effect of DS was hydrogen bonding (H-bonding) interaction. The hydroxyl groups (OH) and bridging oxygen (SiOSi) of DS can form H-bonds with the amine groups of g-C₃N₄ particles and sulfonamides, therefore soluble DS can act as a bridge to enhance the transfer and adsorption of SMZ onto the surface of g-C₃N₄ particles. The presence of DS did not change the mechanism of photodegradation, but there was an optimal concentration for DS to achieve the strongest enhancing effect. H-bonding effect was also found for other oxyanions derived from weak acids, such as silicate, dihydrogen phosphate and borate ions, because the partial ionization of these oxyanions allowed the existence of hydroxyl groups to form H-bonds. The present study not only deepens our understanding of the interface process of the photodegradation of sulfonamides in g-C₃N₄ aqueous suspension, but also provides a potential method to enhance the photocatalytic degradation of antibiotics in wastewater streams.

Peroxymonosulfate improved photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composite under visible light irradiation

The photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composites with peroxymonosulfate (PMS) was investigated under visible light irradiation. The photocatalysts were prepared at different activated carbon (AC) loaded percentages and characterized by XRD, FT-IR, BET surface area, SEM, UV-Vis absorbance, photocurrent response and EIS. Several parameters which might influence the degradation efficiency were studied including PMS concentration, solution pH, catalyst dosage, initial atrazine concentration as well as water matrix effect. The results indicated that incorporation of AC contributes effectively in suppressing the recombination of electron-holes pairs and enhancing the photocatalytic performance of graphitic carbon nitride. More significantly, the degradation efficiency of atrazine showed remarkable improvement with PMS addition under visible light irradiation. The reaction rate constant of the 10% AC/g-C₃N₄/Vis/PMS system (0.0376 min^-1) was approximately 2.9 times higher than that of g-C₃N₄/Vis/PMS system (0.0128 min^-1). Results from quenching tests revealed that both sulfate and hydroxyl radicals were involved in the degradation of atrazine, while the latter is the main contributor. This paper constitutes an insight for the metal-free catalyst activation of PMS by photocatalysis for environmental remediation.

Visible Light Driven Organic Pollutants Degradation with Hydrothermally Carbonized Sewage Sludge and Oxalate Via Molecular Oxygen Activation

Converting sewage sludge into functional environmental materials has become an attractive sewage sludge disposal route. In this study, we synthesize a sewage sludge-based material via a facile one-pot hydrothermal carbonization method and construct a visible light molecular oxygen activation system with hydrothermally carbonized sewage sludge (HTC-S) and oxalate to degrade various organic pollutants. It was found that iron species of HTC-S could chelate with oxalate to generate H₂O₂ via molecular oxygen activation under visible light, and also promote the H₂O₂ decomposition to produce ^•OH for the fast organic pollutants degradation. Taking sulfadimidine as the example, the apparent degradation rate of HTC-S/oxalate system was almost 5-20 times that of iron oxides/oxalate system. This outstanding degradation performance was attributed to the presence of iron-containing clay minerals in HTC-S, as confirmed by X-ray diffraction measurements and Mössbauer spectrometry. In the oxalate solution, these iron-containing clay minerals could be excited more easily than common iron oxides under visible light, because the silicon species strongly interacted with iron species in HTC-S to form Fe-O-Si bond, which lowered the excitation energy of Fe-oxalate complex. This work provides an alternative sewage sludge conversion pathway and also sheds light on the environmental remediation applications of sewage sludge-based materials.

Photochemistry of Hydrochar: Reactive Oxygen Species Generation and Sulfadimidine Degradation

Biochar, mainly including pyrochar produced via pyrolysis of biomass at moderate temperatures of 350-700 °C and hydrochar formed by hydrothermal carbonization in a range of 150-350 °C, has received increasing attention because of its significant environmental impacts. It is known that pyrochar can generate reactive oxygen species even in the dark owing to the presence of persistent free radicals, but hydrochar is far less studied. In this study, we systematically investigate the photochemistry of hydrochar and check its effects on the sulfadimidine degradation. Different from pyrochar derived from the same biomass, hydrochar could generate much more H₂O₂ and •OH under daylight irradiation, which could enhance the sulfadimidine degradation rate six times more than that found in the dark. Raman spectroscopy, Fourier transform infrared spectroscopy, electron paramagnetic resonance, and X-ray photoelectron spectroscopy were employed to elucidate this interesting phenomenon. Characterization results revealed that the higher reactive oxygen species generation ability of hydrochar under solar light irradiation was attributed to its abundant photoactive surface oxygenated functional groups. This study clarifies the differences of pyrochar and hydrochar on organic pollutant degradation, and also sheds light on environmental effects of hydrochar.