Bioinspired Fabrication of Ca-ZnO/CuO/Alginate Beads for Enhanced Wastewater Treatment and Antibacterial Applications

Pure and Ag-decorated ZnO nanoparticles (NPs) were synthesized using a two stage of modified sol-gel technique on microsized substrates, namely sand particles in an effort to prevent agglomeration during photocatalytic reactions. It was found that ZnO NPs can be grown efficiently on sand particles with good adhesion due to the presence of nanosized pits and cracks on the sand surface. The photocatalytic activity of supported pure ZnO NPs was compared to that unsupported pure ZnO NPs of similar size based on the photodegradation of methylene blue (MB) under UV light irradiation. For pure ZnO NPs, the photodegradation rate constant, k recorded for supported sample was found to be 8.6 × 10−3 min−1, being twice the value of that unsupported sample. Meanwhile, the presence of Ag-content that decorated on ZnO NPs has shown gradual increase in rate constants of Ag/Zn ratios from 0.08 to 1.39. The two rate constant values, k1 and k2 have all been observed for each Ag-decorated samples, having k2 greater than that k1 in all such cases. This can be explained by the accelerated degradation activities at lower MB concentrations. In summary, the efficiency of growing pure and Ag-decorated ZnO NPs on sand particles have therefore enhanced the photodegradation capabilities over pure ZnO which due to the prevention of agglomeration in the supported samples.

Degradation by photo-Fenton process using Fe-clay as heterogeneous catalyst under sunlight and microwave irradiation

Caffeine-alginate immobilized CeTiO4 bionanocomposite for efficient photocatalytic degradation of methylene blue

This research aims to decolorize methylene blue using TiO2-Fe photocatalyst and analyze the effect of catalyst doses and pH. Methylene blue was irradiated for 30, 60, 90, 120, 150, 180, 210, and 240 minutes, with methylene blue initial concentrations of 5, 10, 15, and 20 mg/L. The TiO2-Fe was prepared by the sol-gel method. The type of light used is halogen lamp and sunlight. The highest activity is observed at 5 mg/L of dye concentration with catalyst doses 3 g/ L sample solution, pH solution 5, and irradiation time 240 minutes. This final methylene blue concentration after photodegradation under halogen light was 0.4 mg/L (91.89%), while sunlight irradiation the highest %D was 95.63 with final methylene blue concentration 0.22 mg/L. The average %D under sunlight exposure reached (92.63±3.29) % in the clear sky. For optimum process, dye decolorization under sunlight irradiation should be conducted at clear sky due to the high-intensity sunlight irradiation.

Zero valent Ag deposited TiO2 for the efficient photocatalysis of methylene blue under UV-C light irradiation

Antimicrobial efficacy of methylene blue-mediated photodynamic therapy on titanium alloy surfaces in vitro.

Methylene blue (MB) concentrations in residual water were detected using fractional calculus, the Rössler chaotic attractor and laser systems. A Nd:YVO4 nanosecond pulsed laser at 532 nm, with pulse energies ranging from 2 µJ to 7 µJ, was applied to irradiate different water samples containing MB concentrations from 20 µl to 100 µl. Fractional calculus was employed with the purpose of modeling the temperature distribution in the samples, with the Caputo fractional derivative describing photothermal effects induced by laser irradiation. Different MB concentrations were detected by using the Rössler chaotic attractor, it monitored variation on concentrations, associating attractor shapes with MB concentrations. Lower concentrations showed a weaker attractor response, whereas higher concentrations manifest stronger attractor shapes in magnitude. Raman spectroscopy confirmed the detection of MB in residual water from the Requena dam, located in Tepeji del Río de Ocampo, Hidalgo, Mexico. The application of fractional calculus improved the prediction of heat distribution in the samples, by incorporating numerical simulation. The results suggest that this approach is suitable for real-time monitoring, as it associates MB concentrations with distinct chaotic attractor shapes. This technique shows promise for the detection of other contaminants as well. Future research should focus on refining this method and expanding its application to develop innovative monitoring solutions.

Sonochemical synthesis was used to create novel solar light active Mg‐doped CuO nanoparticles. Through a chemical impregnation method, the produced nanomaterial was changed with PVA (polyvinylalcohol). The optical properties, crystal structure, and surface morphologies of the synthesized nanomaterials were probed by UV‐visible spectroscopy (UV‐vis‐DRS), Fourier transform infrared spectroscopy (FT‐IR), Raman spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HR‐TEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), thermogravimetric analysis (TGA), and BET specific surface area studies. The prepared nanomaterials were utilized for the photocatalytic destruction of methylene blue (MB). The photocatalytic activity of PVA‐modified Mg‐doped CuO nanocomposite is magnificent to CuO and Mg‐doped CuO nanomaterials. This is because of the remarkable electron‐hole dissociation and overwhelming increased photocatalytic activity achieved through surface modification. Additionally, the consequence of several reaction factors like pH, catalyst dosage, and MB concentration was deliberated. This research could lead to the development of polymer‐based metal oxide‐doped catalysts for the decomposition of organic contaminants in wastewater.

The objective of this study was to determine the effects of methylene blue (MB) concentration, laser fluence rate, and laser fluence on the efficacy of invitro photodynamic therapy (PDT) for four bacteria commonly found in human abscesses. PDT experiments were performed with four of the most common bacteria found in abdominal abscesses: Escherichia coli, Enterococcus faecalis, Staphylococcus aureus, and Pseudomonas aeruginosa. MB concentration was varied from 50 to 300 μg/mL, and the laser fluence rate was varied from 1 to 4 mW/cm2 at a fluence of 7.2 J/cm2. Higher fluence rates and fluences were explored for P. aeruginosa. Primary outcomes were the reduction in colony-forming units (CFU) following PDT and measured MB uptake following drug incubation. Gram-positive bacteria (E. faecalis and S. aureus) were eradicated at all MB concentrations and laser fluence rates tested. Efficacy was reduced for E. coli but still resulted in >6 log10 reduction in CFU when MB concentration was at least 100 μg/mL. P. aeruginosa required higher fluence (28.8 J/cm2) to achieve comparable efficacy, while increasing fluence rate did not have a significant effect on PDT efficacy. MB uptake was reduced in Gram-negative species compared to Gram-positive species, particularly P. aeruginosa, although uptake was not significantly correlated with CFU reduction. Gram-positive bacteria can be eradicated invitro with low levels of MB (50 μg/mL), laser fluence (7.2 J/cm2), and laser fluence rate (1 mW/cm2). E. coli showed substantial cell killing (>6 log10 CFU reduction) with these same parameters. Low MB uptake and PDT efficacy in P. aeruginosa could be overcome by increasing the laser fluence, while increasing fluence rate did not have an effect.

In this work, a photocatalytic nanocomposite, Fe-doped ZnO/nanocellulose, was synthesized using an in-situ method and examined for methylene blue (MB) degradation. For this purpose, pure ZnO (PZ) was synthesized by the chemical precipitation method and then subjected to Fe+3 doping with different concentrations of Fe3+ (1, 3, and 5 mol%). The PZ and Fe-doped ZnO (FZ) samples were characterized using several standard analyses. UV–Vis DRS analysis was also used to investigate the effect of Fe3+ doping on the bandgap of PZ. The doping of Fe3+ enhanced the photocatalytic activity of ZnO under visible light. The degradation efficiency of FZ samples (> 50%) was enhanced compared to the pristine ZnO (36.91%) during the same period. The catalyst with the highest degradation efficiency (94.21%) was then conjugated with broom corn stalk-derived nanocellulose (NC) at varying NC/Zn2+ molar ratios (0.1, 0.2, 0.3, and 0.4) and characterized by various analyses. The NC enhanced the hydroxyl group at the surface of the nanocomposite, consequently improved the photocatalytic performance of the synthesized samples. The ability of the optimized photocatalyst for MB degradation was assessed. The effect of operating parameters such as pH, catalyst dosage, and initial MB concentration was investigated and degradation efficiency of 98.84% was achieved at the optimum condition. Besides, photocatalyst regeneration study indicated the great photocatalytic performance of this nanocomposite with no loss in its degradation efficiency. The facile synthesis and fast degradation rate of this nanocomposite make it a promising candidate for real-world wastewater treatment.Graphical abstract

Methylene blue (MB) is widely used as a test material in photodynamic therapy and photocatalysis. These applications require an accurate determination of the MB concentration as well as the factors affecting the temporal evolution of the MB concentration. Optical absorbance is the most common method used to estimate MB concentration. This paper presents a detailed study of the dependence of the optical absorbance of aqueous methylene blue (MB) solutions in a concentration range of 0.5 to 10 mg·L-1. The nonlinear behavior of optical absorbance as a function of MB concentration is described for the first time. A sharp change in optical absorption is observed in the range of MB concentrations from 3.33 to 4.00 mg·L-1. Based on the analysis of the absorption spectra, it is concluded that this is due to the formation of MB dimers and trimers in the specific concentration range. For the first time, a strong, thermally induced discoloration effect of the MB solution under the influence of visible and sunlight was revealed: the simultaneous illumination and heating of MB solutions from 20 to 80 °C leads to a twofold decrease in the MB concentration in the solution. Exposure to sunlight for 120 min at a temperature of 80 °C led to the discoloration of the MB solution by more than 80%. The thermally induced discoloration of MB solutions should be considered in photocatalytic experiments when tested solutions are not thermally stabilized and heated due to irradiation. We discuss whether MB is a suitable test material for photocatalytic experiments and consider this using the example of a new photocatalytic material-boron oxynitride (BNOx) nanoparticles-with 4.2 and 6.5 at.% of oxygen. It is shown that discoloration is a complex process and includes the following mechanisms: thermally induced MB photodegradation, MB absorption on BNOx NPs, self-sensitizing MB photooxidation, and photocatalytic MB degradation. Careful consideration of all these processes makes it possible to determine the photocatalytic contribution to the discoloration process when using MB as a test material. The photocatalytic activity of BNOx NPs containing 4.2 and 6.5 at.% of oxygen, estimated at ~440 μmol·g-1·h-1. The obtained results are discussed based on the results of DFT calculations considering the effect of MB sorption on its self-sensitizing photooxidation activity. A DFT analysis of the MB sorption capacity with BNOx NPs shows that surface oxygen defects prevent the sorption of MB molecules due to their planar orientation over the BNOx surface. To enhance the sorption capacity, surface oxygen defects should be eliminated.

Structural, optical and photocatalytic properties of hafnium doped zinc oxide nanophotocatalyst

Methylene blue (MB) is one of the commonly used dyes in the textile industry and can be used as a model pollutant for the textile industry wastewater. In this work, the photocatalytic degradation of MB by synthesized nanoparticles of lanthanum vanadate (LaVO4) was assessed. The effects of pH, initial MB concentration and catalyst dose on the removal performance of MB were investigated and measuring the optimum values of these operational conditions was performed using response surface methodology (RSM). Catalyst dose of 0.43 g/L, initial MB concentration of 5.0 mg/L, and pH of 6.86 were found to be the optimum conditions in reaction time of 60 min. A mathematical model was formed to relate the removal efficiency of MB to the aforementioned operating parameters. The removal efficiency of MB was 91% without any scavengers at a catalyst dose of 0.3 g/L, pH of 7 and initial MB concentration of 10 mg/L. The trapping experiments confirmed the participation of different reactive species in the photo-degradation process. The degradation rates of MB were 91%, 86%, 81%, 77.70% and 72% in five successive runs using LaVO4.

In this study, a model to improve the degradability of methylene blue (MB) dye using graphene oxide/TiO2/SiO2 nanocomposite under sunlight irradiation is investigated. The effect of operative parameters comprising catalyst concentration, initial dye concentration, and pH on the photocatalytic batch during removal of MB is studied. Fractional factorial design (FFD) and response surface methodology (RSM) are used to design the experiment layout. Graphene oxide (GO)/TiO2/SiO2 nanoparticles are synthesized through sonication and sol–gel methodologies. In the experiments, three levels of catalyst varied in the percentage of TiO2 pointed as (I) TiO2:GO (100%), (II) TiO2:GO:SiO2 (50%), and (III) TiO2:GO:SiO2 (25%) are used. The irradiation interval was 7 h at solar radiation energy 6.35–5.00 kW h/m2/day. In the experiments, three levels of catalyst varied in the percentage of TiO2 pointed as (I) TiO2:GO (100%), (II) TiO2:GO:SiO2 (50%), and (III) TiO2:GO:SiO2 (25%) are used. The synthesized catalysts are characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscope, and X-ray photoelectron spectroscopy. ANOVA under 23 FFD is conducted to evaluate the effect of independent factors depending on the value of F as pH of solution, weight of catalyst, and concentration of MB. The adsorption kinetics, experimental design with FFD, and RSM are investigated in this study. The Surface Adsorption kinetics were statistically analyzed, the model that best described the results of each experiment was determined out of the two evaluated kinetics (pseudo-first order, pseudo-second order), for the three photocatalyst composites I, II, and III with the parameters; weight of the catalyst, pH, and initial MB concentration, also percentage degradation is evaluated. RSM results are consistent with the kinetic model; first, the pH is considered as the most significant parameter affecting the removal of the organic pollutant, and second, catalyst II gives the highest percentage removal efficiency of MB. FFD results are consistent with both models where the effect of the independent factor depending on the value of F was pH of solution > weight of catalyst > initial concentration of MB. The percentage removal was in the range from 30 to 99%.

This study describes the preparation of zinc oxide nanocomposite and its application as photocatalyst in the degradation of methylene blue under sunlight irradiation. Zinc oxide-coated biochar (ZnO/BC) nanocomposite was prepared using the hydrothermal method from banana peels and zinc acetate dihydrate as precursors. The biochar (BC), ZnO nanoparticles (ZnONPs), and ZnO/BC nanocomposite were characterized, and the results showed that ZnONPs had definite crystallinity and a regular surface morphology, with particles approximately 18 nm in size, and a XRD pattern corresponding to ZnONPs. In contrast, the ZnO/BC nanocomposite exhibited a more amorphous structure consistent with wurtzite (ZnO) and an irregular surface morphology with clusters of white particles measuring around 20–30 nm. Tauc’s plot was used to calculate the band gaps energy of ZnONPs (3.04 eV) and ZnO/BC nanocomposite (2.89 eV). Catalyst-free, ZnONPs, and ZnO/BC nanocomposite were utilized for the photocatalytic degradation of methylene blue (MB) under sunlight irradiation for 0 to 120 min in which ZnO/BC nanocomposite showed excellent photocatalytic degradation of MB under sunlight irradiation at 0 to 120 min due to lower band gap energy and synergetic effect between ZnO and BC. Dosages of 100 mg (ZnO/BC nanocomposite) and 10 ppm (MB) were optimized to obtain the best photocatalytic degradation efficiency (92 %) under sunlight irradiation with 0 to 120 min. The process was conducted with various parameters like dosage variation, concentration of MB, and different pH 3, 5, 8, and 10 to improve the photocatalytic degradation of MB from wastewater. The results indicated that the optimal conditions for the photocatalytic degradation of MB (92% after 120 min) were a catalyst dosage of 100 mg, an MB concentration of 10 ppm, and a pH of 10. This work demonstrates the potential of ZnO/BC nanocomposite photocatalyst for application in wastewater treatment and environment remediation.