Effect Of Water Matrix Research Articles

Photocatalytic performance of 3D engineered chitosan hydrogels embedded with sulfur-doped C3N4/ZnO nanoparticles for Ciprofloxacin removal: Degradation and mechanistic pathways.

Ciprofloxacin, a biotoxic micropollutant, is ubiquitously found in the water environment, which is a global concern. This study developed polymeric S-C3N4/ZnO-Chitosan (indexed as SCZ-CH) hydrogels for degrading Ciprofloxacin. The SCZ-CH hydrogels provided the Ciprofloxacin degradation efficiencies of ~93% and ~69% in UV and visible lights, respectively, at optimum conditions (SCZ-CH hydrogels with 2g/L SCZ, 20mg/L initial concentration, pH5, and room temperature). In addition, immobilized SCZ-CH hydrogels structures enable easy separation of the SCZ catalyst from water. The spectroscopic and microscopic analyses of SCZ-CH hydrogels show multifaceted properties, like high oxygen concentrations, crystallinity, stacked structure, high roughness, and improved bandgap energy, which are responsible for the enhanced photocatalytic activity. The effects of water matrix and experimental conditions on Ciprofloxacin degradation were also studied, which suggested that the catalyst dose and solution pH have significant effects on photocatalytic activity. SCZ-CH hydrogels have shown good mineralization efficiency (~98%) and reusability (up to 10cycles) for Ciprofloxacin removal. Superoxide radicals played an essential role in the degradation of Ciprofloxacin. The Ciprofloxacin molecules get degraded by driving radicals through oxidation, defluorination, substitution, and breaking of the rings. The proposed SCZ-CH hydrogels can be effectively used at a large scale to treat micropollutants.

Removal of microcontaminants by zero-valent iron solar processes at natural pH: Water matrix and oxidant agents effect

This work deals with microcontaminants (MCs) removal by natural solar zero-valent iron (ZVI) process at natural pH in actual matrices. Commercial ZVI microspheres were selected as ZVI source and hydrogen peroxide and persulfate were used as oxidant agents. The experimental plan comprised the evaluation of sulphates and carbonates/bicarbonates effect on process performance, the possibility of adding an iron chelate (EDDS) to take advantage of leached iron and the treatment of MCs in actual MWWTP secondary effluent. The presence of sulphates and EDDS addition did not lead to significant changes in the process efficiency, while the carbonates naturally present in natural water (458 mg/L) diminished the treatment time need to reach the decontamination goal. Finally, the treatment of a MCs mixture consisting of Atrazine, Carbendazim, Imidacloprid, and Thiamethoxam in the range of μg/L in actual MWWTP secondary effluent by solar/msZVI/H2O2 and solar/msZVI/S2O82− obtained 7 and 22% of total removal after 180 min, respectively, which indicated a moderate competitiveness of these processes with respect to other advanced oxidation processes.

Degradation of Organics and Formation of Dbps in the Combined Led-Uv and Chlorine Processes: Effects of Water Matrix and Fluorescence Analysis

Degradation of Organics and Formation of Dbps in the Combined Led-Uv and Chlorine Processes: Effects of Water Matrix and Fluorescence Analysis

HCO3–/CO32– enhanced degradation of diclofenac by Cu(Ⅱ)-activated peracetic acid: Efficiency and mechanism

• HCO 3 – /CO 3 2– significantly enhanced the degradation of DCF by Cu(Ⅱ)-activated PAA. • The highest removal efficiency of DCF was obtained at [HCO 3 – ] 0 : [CO 3 2– ] 0 = 9:1. • Organic radicals CH 3 C(=O)O• and CH 3 C(=O)OO• were mainly responsible for DCF removal. • CuCO 3 and CuCO 3 (OH) − might be the major Cu(Ⅱ) species to activate PAA. • Effective DCF degradation was achieved at a low Cu(Ⅱ) dose (<15 μM) in this system. Diclofenac (DCF), a non-steroidal anti-inflammatory drug, is an emerging and nonbiodegradable contaminant which is detected extensively in aquatic environment. Therefore, low cost and efficient method for DCF degradation has been the aim of many studies. In this study, DCF was efficiently removed by Cu(II)/peracetic acid (PAA) system in the presence of bicarbonate (HCO 3 – ) and carbonate (CO 3 2– ). The concentration ratio of HCO 3 – to CO 3 2– was found to have a significant effect on DCF removal, and the highest removal efficiency of DCF was obtained at [HCO 3 – ] 0 : [CO 3 2– ] 0 = 9:1 due to the formation of CuCO 3 and CuCO 3 (OH) − . According to the results of scavenging experiments and electron paramagnetic resonance (EPR), organic radicals (CH 3 C(=O)OO • and CH 3 C(=O)O • ) were considered to be mainly responsible for DCF degradation in Cu(Ⅱ)–HCO 3 – (CO 3 2– )/PAA system. Operational parameters including initial PAA concentration and Cu(Ⅱ) dosage were optimized for DCF removal, and effect of common water matrix (i.e., natural organic matter, SO 4 2− , NO 3 – and Cl − ) on DCF degradation were systematically investigated. Finally, based on the detected degradation products, five probable degradation pathways of DCF were proposed including hydroxylation, decarboxylation, formylation, dehydrogenation and C-N bond cleavage.

Safe drinking water for rural communities using a low-cost household system. Effects of water matrix and field testing

The relationship between turbidity (T) and ultraviolet C (UVC) disinfection is still not clearly understood, as well as no attention has been paid to the contribution of natural organic matter (NOM). The present work assessed the influence of particulate and NOM on the UVC disinfection efficiency in terms of E. coli and MS2 removal at bench collimated beam (CB) and flow-UVC systems, both in the laboratory and in the field (Colombia). The flow-UVC reactor was installed as part of a household water treatment (HWT) system consisting of filtration + UVC disinfection. Tests were performed according to the WHO standards using fine test dust, humic acid (HA), and MS2 and E. coli as microbiological indicators. CB results showed a significant decrease in the inactivation rate of MS2 in the presence of small concentrations of HA (3.5 mg/L), with killing dose increasing a 65%, vs. non-significant effects of turbidity in the range of 0–20 NTU. Following the same trend, in flow-UVC tests the inactivation efficiency of MS2 decreased solely in the presence of HA. At the same HA concentration and flow rate, an increase in turbidity of 17.6 NTU showed a negligible effect. Conversely, in the presence of HA, UVT254 dropped from 88.7% (0 mg/L HA) to 73.3%, reducing MS2 inactivation by 1–2 log-units. Finally, the HWT system could be classified as protective working at flow rates ≤5 L/min. However, in the presence of 3.5 mg/L HA (UVT254 < 75%), it presented a limited protection for viruses.

Photocatalytic ozonation in water treatment: Is there really a synergy between systems?

Numerous studies report on the synergy between ozonation and photocatalytic oxidation (TiO2/UVA), which could open the way to the application of photocatalytic ozonation (PCOz) in water treatment. With the aim of establishing the existence of this synergy and its origin, in this work, using TiO2 P25, 365 nm UVA LEDs and ozone transferred doses up to 5 mg (mg DOC0)−1 (DOC0 7 – 10 mg L−1), a systematic study has been carried out featuring the effect of pH, alkalinity and water matrix in each of the systems involved in PCOz, with special attention to the role of organics adsorption onto TiO2. In ultrapure water, an increase in pH and carbonates content exerted a slight negative effect on the photocatalytic degradation of primidone (low adsorption onto TiO2 and mainly abated by free HO•), this effect being higher on its mineralization. The negative effect of pH and alkalinity was much stronger for oxalic acid (high tendency to adsorb and mainly oxidized by positive holes). Accordingly, the results obtained at pH < pHpzc (point of zero charge of the catalyst) in ultrapure water cannot at all be extrapolated to secondary effluents, since their composition negatively affects the photocatalytic performance. At the experimental conditions applied, only for the secondary effluent a synergy between O3/UVA and TiO2/UVA systems was observed. This synergy would be related, on the one hand, to the generation, from the matrix itself, of reactive entities or intermediates that promote the decomposition of ozone into HO•; and, on the other hand, to an increase in catalyst activity as the matrix UVA absorption decreases, rather than from direct interactions between both systems. Despite de above, ozone requirement to achieve a significant reduction of DOC is high and would only be an interesting strategy for the elimination of ozone-refractory micropollutants.

Enhanced removal of perfluorooctane sulfonic acid and perfluorooctanoic acid via polyelectrolyte functionalized ultrafiltration membrane: Effects of membrane modification and water matrix

This study investigated the mechanisms of removal of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) using polyelectrolyte (PE) functionalized ultrafiltration (UF) membranes, performed through a fluidic method of layer-by-layer (LbL) deposition of polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) multilayer coatings. The effects of source water composition (humic acids [HA] and cations [Ca2+ and Mg2+]) on PFOS and PFOA removal efficiency by the functionalized membrane were determined. PAH/PAA modification resulted in approximately 38 % and 9.2 % reduction in membrane molecular weight cut-off (MWCO) and porosity, respectively, leading to approximately 30 % increase in the removal of PFOS and PFOA primarily due to size exclusion. The presence of only HA led to 10–12 % higher removal of PFOS/A when compared to DI water; however, an increase in HA concentration did not further influence their removal efficiency. The coexistence of cations and HA resulted in significantly higher removal of PFOS and PFOA (up to 23 % higher for PFOS). Further enhancement of PFOS removal (14 % higher) was observed when cation concentrations were doubled, attributable to the interactions of PFOS/A with the source water components and the functionalized membrane, resulting in enhanced size and charge exclusion of macromolecular complexes including PFOS-cation-PFOS, PFOS-cation-HA, and PFOA-cation-HA.

Treatment of PPCPs and disinfection by-product formation in drinking water through advanced oxidation processes: Comparison of UV, UV/Chlorine, and UV/H2O2

The presence of pharmaceutical and personal care products (PPCPs) in water is concerning because of their potential threat to ecosystems and human health. Studies have indicated that these emerging contaminants cannot be effectively removed through conventional water treatment. In this study, the efficacy of various treatments - chlorination, ultraviolet (UV), UV/Chlorine, and UV/H2O2 processes - in PPCP removal from water was compared. The effects of reaction time, oxidant concentration, pH, and water matrix and the generation of disinfection by-products (DBPs) were also assessed. The removal of PPCPs was discovered to be superior when the concentration of oxidants was higher. In addition, pH affected the reactivity of chlorine with some of the investigated chemicals. Chorine itself plays a minor role in the UV/Chlorine process because it serves as a reactant for the generation of free radicals rather than oxidants. Matrix had a weak effect on the removal of PPCPs in the various treatment processes (mostly within 10%). UV could not effectively remove acetylsalicylic acid, ibuprofen, benzophenone, oxybenzone, caffeine, N,N-diethyl-meta-toluamide, or most estrogens. When chlorine or hydrogen peroxide (H2O2) was used with UV, the efficiency of removal of all selected PPCPs was greatly improved (≥56.5% for UV/Chlorine and ≥27.6% for UV/H2O2) within 5 min. Although the PPCP removal efficiency of UV/Chlorine was higher than that of UV/H2O2, UV/H2O2 resulted in smaller amounts of DBP formation in the treated water. By contrast, UV/Chlorine resulted in higher concentrations of trihalomethanes (21.6%), haloacetonitriles (29.4%), and haloketones (147.2%).

Oxidative Degradation of Tetracycline by Magnetite and Persulfate: Performance, Water Matrix Effect, and Reaction Mechanism.

This study presents a strategy to remove tetracycline by using magnetite-activated persulfate. Magnetite (Fe3O4) was synthesized at high purity levels—as established via X-ray diffractometry, transmission electron microscopy, and N2 sorption analyses—and tetracycline was degraded within 60 min in the presence of both magnetite and persulfate (K2S2O8), while the use of either substance yielded limited degradation efficiency. The effects of magnetite and persulfate dosage, the initial concentration of tetracycline, and the initial pH on the oxidative degradation of tetracycline were interrogated. The results demonstrate that the efficiency of tetracycline removal increased in line with magnetite and persulfate dosage. However, the reaction rate increased only when increasing the magnetite dosage, not the persulfate dosage. This finding indicates that magnetite serves as a catalyst in converting persulfate species into sulfate radicals. Acidic conditions were favorable for tetracycline degradation. Moreover, the effects of using a water matrix were investigated by using wastewater treatment plant effluent. Comparably lower removal efficiencies were obtained in the effluent than in ultrapure water, most likely due to competitive reactions among the organic and inorganic species in the effluent. Increased concentrations of persulfate also enhanced removal efficiency in the effluent. The tetracycline degradation pathway through the magnetite/persulfate system was identified by using a liquid chromatograph-tandem mass spectrometer. Overall, this study demonstrates that heterogeneous Fenton reactions when using a mixture of magnetite and persulfate have a high potential to control micropollutants in wastewater.

A comparative study on the degradation of phenylurea herbicides by UV/persulfate process: Kinetics, mechanisms, energy demand and toxicity evaluation associated with DBPs

The degradation performance of selected phenylurea herbicides (isoproturon and chlorotoluron) by UV/persulfate (PS) as well as toxicity assessments associated with disinfection by-products (DBPs) in subsequent oxidation were comparatively studied. The elimination of herbicides followed pseudo first-order kinetics well. Then effects of UV intensity, pH, PS dosage and water matrix (background ions and Nature organic matter (NOM)) were investigated detailedly. Increased kobs values were observed at higher PS dosages and greater UV intensity, but the degradation was basically resistant to pH variation. kobs could be inhibited by coexistent ions and NOM. Radical scavenging study revealed the more important role of sulfate radical (SR, SO4•−) than hydroxyl radical (HR, HO•). kapp of HO• and SO4•− towards isoproturon and chlortoluron were determined respectively. The results also indicated that the relative reactivity of alkyl- or halogen- substituted phenylurea herbicides with HO• and SO4•− can be correlated with Hammett constants as the molecular descriptor. Then a quantitative structure-activity relationship was established to predict the structure-dependent reactivity of phenylurea herbicides by UV/PS concerning substituent effects. The energy demand of UV/PS system was evaluated. The degradation intermediates by direct UV, UV/H2O2 as well as UV/PS were comparatively identified and the related destruction pathways were postulated. Compared with UV and UV/H2O2, UV/PS was superior in controlling the DBPs generation in post-disinfection of these herbicides. The data supported that SR-advanced oxidation processes (AOPs) had more advantages in removal efficiency and toxicity control than HR-AOPs. This study provided some theoretical bases for the UV/PS degradation behaviors of structurally similar phenylurea herbicides with regard to different substituents on the aromatic ring.

Modeling degradation kinetics of gemfibrozil and naproxen in the UV/chlorine system: Roles of reactive species and effects of water matrix

The UV/chlorine system has been regarded as an efficient oxidation technology for the removal of aqueous micropollutants. However, the roles of the possible radical species for this system on the elimination under environmentally relevant conditions/real waters were still largely unknown. Herein, the specific roles of radical species in the UV/chlorine oxidation degradation of gemfibrozil and naproxen as representative micropollutants were quantified by a steady-state kinetic prediction model considering the effects of water matrices. Overall, the model predicted results are consistent with the experimental data well. •OH and reactive chlorine species (RCS, such as Cl•, ClO•, and Cl2•−) contributions to gemfibrozil and naproxen degradation were water matrix specific. In pure water, both primary reactive species (i.e., •OH and Cl•) and secondary species ClO• dominated gemfibrozil and naproxen degradation, and their individual and the sum of the contributions to degradation rates reduced with pH increase of from 5 to 9. In the presence of Cl−, we found that Cl2•− and in particular ClO• were responsible for the enhanced degradation with increasing Cl− concentrations due to the considerable ClO• reactivity of gemfibrozil (1.93 × 109 M−1 s−1) and naproxen (9.24 × 109 M−1 s−1) and the rapid transformation of Cl2•− to ClO•. The presence of HCO3− notably facilitated the degradation in the UV/chlorine process because of the generation of CO3•−. CO3•− showed high reactivity with gemfibrozil and naproxen corresponding to respective second-order reaction rate constants of 2.45 × 107 and 3.50 × 107 M−1 s−1. Dissolved organic matter induced obvious scavenging for •OH, Cl•, and ClO• and greatly retarded the degradation. The constructed model considering the effects of above water matrix has successfully predicted the oxidation degradation kinetics in real waters, and both •OH and CO3•− are the predominant reactive species in the degradation. This study is helpful for comprehensive understanding the roles of possible radical species in micropollutant removal by UV/chlorine oxidation under real water matrix.

Magnetic copper smelter slag as heterogeneous catalyst for tetracycline degradation: Process variables, kinetics, and characterizations.

The treatment of solid wastes and wastewater for sustainable development has been a hot topic. This work proposes a novel process of “waste treating waste” using magnetic copper smelter slag (CSS) as heterogeneous catalyst. The effect of process variables and water matrix was studied on catalytic performance. Under conditions of CSS 10 g/L, H2O2 100 mM, pH 4.4, and temperature 25 °C, tetracycline can be effectively degraded within 30 min. The apparent rate constant is comparable to or higher than previous reports, and the activation energy is 37 kJ/mol. The broad operation pH, slight effect of water matrix, and magnetic property of CSS are favorable for potential application. CSS was characterized by N2 adsorption-desorption isotherm, SEM-EDS, XRD, XPS, ICP and zeta potential. The dominant components of CSS are fayalite and magnetite, and the major metals of Fe and Cu provide active sites for H2O2 activation. Hydroxyl radical generated by H2O2 activation is dominant oxidative specie for tetracycline degradation. The plausible mechanism of tetracycline degradation in the solution and on catalyst surface is proposed.

Prussian blue immobilized on covalent organic polymer-grafted granular activated carbon for cesium adsorption from water

Technologies for removing radioactive waste in the form of 137Cs, released during nuclear power plant accidents, are essential. Prussian blue (PB) is a pigment with a face-centered cubic structure that can selectively adsorb cesium. However, due to its very small size (5–200 nm), PB can be found in water as a fine powder and it is difficult to separate its disposal to the water system. Thus, in this study, PB was immobilized on granular activated carbon (GAC), normally used for water treatment, to facilitate its recovery after usage. The GAC surface was grafted with a covalent organic polymer (COP) to improve its stability and prevent PB desorption. The COP-grafted GAC immobilized approximately twice as much PB as the ungrafted one; its cesium adsorption capacity was over three times higher and the PB stability was excellent. The effects of pH and water matrix were investigated using samples of both artificial and actual river water. Moreover, a continuous column experiment was conducted to evaluate the applicability of the proposed material in water treatment system in a form of GAC column.

Degradation of carbamazepine by UVA/WO3/hypochlorite process: Kinetic modelling, water matrix effects, and density functional theory calculations

The rapid recombination of electron/hole pairs is a major setback in the application of WO3-based photocatalysis in water treatment. In this study, hypochlorite (ClO−) was used as an electron acceptor to enhance the photocatalytic degradation of carbamazepine (CBZ) using UVA-excited WO3. The results showed that CBZ degradation in the UVA/WO3/ClO− system followed a pseudo-first order reaction kinetic model. The addition of 0.1 mM ClO− to the UVA/WO3 system at pH values of 8.2 and 6.2 increased the rate constant (kobs) of the degradation process 5.3- and 11.5-fold, respectively. Further, increasing the WO3 dosage or decreasing the initial CBZ concentration resulted in an increase in kobs. However, at high concentrations, ClO− inhibited CBZ degradation. Based on the kinetic model, it could be suggested that ClO played a dominant role in the degradation process. Furthermore, the water matrix effects were as follows: the optimal pH was 6.2; humic acid, chloride, bicarbonate, and ammonium exhibited inhibitory effects on CBZ degradation; and sulfate ion significantly enhanced the degradation. Density functional theory (DFT) calculations indicated a strong affinity between ClO− and the WO3 surface. Specifically, the electrical energy per order that was associated with the use of ClO− varied in the range of 0.100–1.617 kWh/m3. In summary, this study shows that ClO− is an excellent electron acceptor for excited WO3, while clarifying the CBZ degradation-enhancing effect of ClO− as well as the kinetic model and DFT calculations. These findings can be employed in the degradation of recalcitrant contaminants in a cost-effective manner, while being significant for the development of more effective catalysts of UV-assisted advanced oxidation processes.

Photocatalytic removal of antibiotics by MOF-derived Ti3+- and oxygen vacancy-doped anatase/rutile TiO2 distributed in a carbon matrix

Residual antibiotic in ecosystems are an environmental problem that urgently needs to be solved. Developing efficient and green photocatalysts is an attractive option for the removal of antibiotics. In this work, a titanium metal organic framework (Ti-MOF) was calcined in an air atmosphere to obtain Ti3+- and oxygen vacancy (Ov)-doped anatase and rutile heterojunction TiO2 (A/R-TiO2) distributed in a carbon matrix. Through XPS, UV–Vis, ESR and other characterizations, it is proven that Ti3+ and Ov exist in heterojunction TiO2. And the characterization results that Ti3+- and Ov-doped A/R-TiO2 exhibits expanded visible light absorption and enhanced separation of charge carries. The photocatalytic degradation efficiency of tetracycline (TC) by the optimal Ti-MOF derived materials reaches 87.03% and the degradation rate of chlortetracycline (CTC) reaches 78.91% in 60 min. When studying the effect of water matrix on the removal of TC, it was found river water has the highest removal rate of TC (70.76%), followed by tap water (66.37%), lake water (61.19%), and hospital wastewater (52.68%). This shows that the carbon coated Ti3+- and Ov-doped A/R-TiO2 is effective for the degradation of antibiotics. In addition, the carbon coating formed by the pyrolysis of the Ti-MOF as a barrier layer can prevent the oxidation of Ti3+ and Ov, which make the prepared materials have good stability and repeatability. In this work, hole (h+) and superoxide radical (•O2−) are the active substances that play a major role in the degradation system, while the effect of hydroxyl radicals (•OH) is small. Finally, a possible mechanism of carbon coated Ti3+- and Ov-doped TiO2 for photocatalytic degradation is proposed.

Construction of MoO3 nanopaticles /g-C3N4 nanosheets 0D/2D heterojuntion photocatalysts for enhanced photocatalytic degradation of antibiotic pollutant

A new type of 0D-2D Z-scheme heterojunction photocatalyst (MoO3/g-C3N4) was successfully prepared via simple hydrothermal calcination method. The catalytic activities of MoO3/g-C3N4 was evaluated by the degradation effect of tetracycline. The results indicated that the 0D-2D MoO3/g-C3N4 Z-scheme heterojunction was significantly better than that of original g-C3N4. Especially, the optimal 0.5 wt% MoO3/g-C3N4 could reach 85.9% removal efficiency within 100 min under visible light irradiation (λ > 420 nm), and its degradation rate constant was 2.3 times higher than that of g-C3N4·In addition, the effects of real water matrix, natural sunlight irradiation on tetracycline removal were examined. Reactive-species-trapping experiments show that both photo-generated •O2− and h+ are the main active species in the photocatalytic process. Besides, the results of •O2− and •OH detection further indicated that the yield amount of •O2− and •OH in MoO3/g-C3N4 case showed enhancement when compared with g-C3N4. Moreover, the quite stable crystal structure and excellent recycling ability endowed the MoO3/g-C3N4 composite with a great potential for applying in photocatalytic fields.

Construction of oxygen vacancy assisted Z-scheme BiO2−x/BiOBr heterojunction for LED light pollutants degradation and bacteria inactivation

It is well known that the most important task of photocatalytic technology is to synthesize photocatalysts with compact heterojunction structure and high redox ability. To achieve the goal, a novel Z-scheme BiO2−x/BiOBr heterojunction containing oxygen vacancy was synthesized by an in-situ generation process. Several techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have verified the BiO2−x/BiOBr heterojunction. XPS and electron spin resonance (ESR) reveals the presence of oxygen vacancy in the BiO2−x/BiOBr composite. As expected, the BiO2−x/BiOBr composite showed good performance in removing Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Rhodamine B (RhB) and tetracycline (TC). The effects of inorganic ions, pH value and water matrix were investigated with many details. The active species and proposed mechanism were revealed by trapping experiment and related characterizations. The synergistic effect of oxygen vacancy and Z-scheme heterojunction makes the BiO2−x/BiOBr composite possess excellent photocatalytic activity.

Different degradation mechanisms of carbamazepine and diclofenac by single-atom Barium embedded g-C3N4: the role of photosensitation-like mechanism

This study reports the different degradation mechanisms of carbamazepine (CBZ) and diclofenac (DCF) by single-atom Barium (Ba) embedded g-C3N4. Single-atom Ba is anchored onto g-C3N4 by forming ionic bond with triazine ring, thus greatly enhances the photocatalytic activity with an atom ratio of 1.78%. CBZ undergoes a typical photocatalysis mechanism, while DCF is degraded via a photosensitization-like process, which does not need band gap excitation of photocatalyst. By means of Density Functional Theory (DFT) calculation, the selectivity is found to be related with the different valence excitation modes of CBZ and DCF. Specifically, CBZ undergoes a local excitation, which does not obviously affect molecular configuration. In contrast, DCF undergoes a charge transfer excitation, which significantly changes the reactive sites distribution and facilitates photosensitization-like degradation. Due to the different degradation mechanism, the effects of pH, co-existed anions, and water matrix are also different. Since photosensitization-like mechanism does not rely on photo-generated holes mediated oxidation, the degradation efficient of DCF shows higher anti-interference capacity in real water.

Facile construction of 2D g-C3N4 supported nanoflower-like NaBiO3 with direct Z-scheme heterojunctions and insight into its photocatalytic degradation of tetracycline

Photocatalytic oxidation using solar energy is a promising green technology to degrade antibiotic contaminants. Herein, a 2D g-C3N4 supported nanoflower-like NaBiO3 with direct Z-scheme heterojunction was synthesized via a facile hydrothermal approach, and the photocatalytic performance of g-C3N4/NaBiO3 was remarkable better than that of g-C3N4 and NaBiO3 for tetracycline degradation under visible light. Photoinduced electrons accumulated on the conduction band of g-C3N4 and holes gathered on the valence band of NaBiO3, which was more suitable for generating superoxide and hydroxyl radicals. Meanwhile, the built-in electric field between g-C3N4 and NaBiO3 was proved by their different work functions based on DFT calculations, which enhanced the charges separation. The formed radicals were determined by ESR, and their role in the degradation of tetracycline was examined by the active species trapping test. Moreover, the sites attacked by free radicals and degradation pathways for tetracycline were inferred by the results of Gaussian 09 program and HPLC-MS. The effects of water matrix and three other organic contaminants was further studied for actual use evaluation. Importantly, the prepared g-C3N4/NaBiO3 showed stable photodegradation activity for eight cycles. This work not only provides a promising photocatalyst, but also gets insight into the photocatalytic removal of tetracycline.

Understanding the effects of mineral water matrix on degradation of several pharmaceuticals by ultrasound: Influence of chemical structure and concentration of the pollutants

Degradation of seven relevant pharmaceuticals with different chemical structures and properties: acetaminophen (ACE), cloxacillin (CXL), diclofenac (DCF), naproxen (NPX), piroxicam (PXC), sulfacetamide (SAM) and cefadroxil (CDX), in distilled water and mineral water by ultrasound was studied herein. Firstly, proper conditions of frequency and acoustic power were determined based on the degradation ability of the system and the accumulation of sonogenerated hydrogen peroxide (24.4 W and 375 kHz were found as the suitable conditions for the sonochemical treatment of the pharmaceuticals). Under such conditions, the pharmaceuticals degradation order in distilled water was: PXC > DCF ~ NPX > CXL > ACE > SAM > CDX. In fact, the initial degradation rate showed a good correlation with the Log P parameter, most hydrophobic compounds were eliminated faster than the hydrophilic ones. Interestingly, in mineral water, the degradation of those hydrophilic compounds (i.e., ACE, SAM and CDX) was accelerated, which was attributed to the presence of bicarbonate ions. Afterwards, mineral water containing six different initial concentrations (i.e., 0.331, 0.662, 3.31, 16.55, 33.1, and 331 µM) of selected pharmaceuticals was sonicated, the lowest concentration (0.331 µM) always gave the highest degradation of the pollutants. This result highlights the great ability of the sonochemical process to treat bicarbonate-rich waters containing pollutants at trace levels, as pharmaceuticals. Finally, the addition of ferrous ions to the sonochemical system to generate a sono-Fenton process resulted in an acceleration of degradation in distilled water but not in mineral water. This was attributed to the scavenging of sonogenerated HO• by bicarbonate anion, which decreases H2O2 accumulation, thus limiting the Fenton reaction.