Lignin derived macromolecular compounds are the main constituents responsible for the hazardous effects of discharged effluents from the pulp and paper industry in receiving waters. It was shown by ultraviolet–visible (UV–vis) and fluorescence spectroscopies that a selective photodegradation of these structures occurred upon irradiation of fulvic acids (FA) from a kraft pulp mill effluent. Though photodegradation was not remarkably affected by the presence of the natural photosensitizer nitrate, it was inhibited under the presence of chloride. These results indicate that the fate of macromolecular organic matter from kraft pulp mill effluents may be different depending on the type of receiving waters, having a higher persistence when effluents are discharged in estuarine or marine waters than when they are discharged in fresh water.

Nanoscaled Bi₂O₃ particles coated on ZnO nanorods (ZNRs) have been fabricated by combining hydrothermal technique with a chemical precipitation method. X-ray diffraction, field emission-scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and UV–vis absorption and photoluminescence studies were adapted to characterize the structure, morphologies, and optical properties of the nanocomposites. The results indicated that small Bi₂O₃ nanoparticles were well distributed on the surfaces of ZNRs. And the Bi₂O₃–ZNR nanocomposites showed high charge separation efficiency and •OH generation ability as evidenced by photoluminescence spectra. Under irradiation of a 55-W compact fluorescent lamp, the Bi₂O₃–ZNR nanocomposites demonstrated photocatalytic activities higher than pure ZNRs in the degradation of two endocrine-disrupting chemicals, phenol and methylparaben, which might be attributed to the high separation efficiency of photogenerated electron–hole pairs based on the cooperative role of Bi₂O₃ loading on ZNRs. Moreover, the Bi₂O₃–ZNR nanocomposite could be easily recovered and reused due to their one-dimensional nanostructural property. All these characteristics brought enormous benefits of Bi₂O₃–ZNR nanocomposites to the practical application in indoor environmental remediation.

The ubiquitous presence of chlorophenols (CPs) continues to be a cause of concern, owing to their recalcitrant nature. In this context, the present work investigated the degradation of model compounds, 4-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, and pentachlorophenol, by an organic oxidant, methyl ethyl ketone peroxide (MEKP) coupled with ultraviolet irradiation in basic media. Chemical analysis was followed by high-performance liquid chromatography and gas chromatography–mass spectrometry. Despite exhibiting varied patterns of decline, chemical oxygen demand was eventually noted to decrease to the extent of up to 70 %. Simultaneous increase/decrease in the release of chloride ions and decrease in pH indicated that parallel reactions were occurring, which led to the formation of acidic reaction products. First-order dynamics was approximated for all CP congener degradation. The degraded compounds showed absolutely no presence of chlorine atoms, which was a noteworthy feature testifying to the fact that MEKP action was capable of detoxification of CP congeners.

Coupled Bi₂O₃/TiO₂ photocatalysts were fabricated by sol–gel and hydrothermal methods and characterized using various spectroscopy techniques. Photocatalytic reduction of Cr(VI) in aqueous solution, together with the synergistic effect of photodegradation of bisphenol A (BPA), was investigated using these coupled Bi₂O₃/TiO₂ under visible-light irradiation. Coupling of Bi₂O₃ inhibited the phase transformation from anatase to rutile and extended absorption region to visible light. Bi ions did not enter TiO₂ lattice and were more likely to bond with oxygen atoms to form Bi₂O₃ on the surface of TiO₂. Photovoltage signals in visible range revealed the effective interfacial charge transfer between Bi₂O₃ and TiO₂. Two percent Bi₂O₃/TiO₂ exhibited the highest photocatalytic activity of visible-light-induced reduction of Cr(VI). The addition of BPA effectively increased the photocatalytic reduction of Cr(VI). Simultaneously, the presence of Cr(VI) promoted the degradation of BPA, which was demonstrated by the investigation of TOC removal yield and generated intermediates. A possible mechanism of photocatalytic reduction of Cr(VI) and degradation of BPA in Bi₂O₃/TiO₂ system was proposed. The synergistic effect, observed between reduction of Cr(VI) and degradation of BPA, provides beneficial method for environmental remediation and purification of the complex wastewater.

Iron and arsenic have been found to coexist in a water environment and the fate of arsenite in the aquatic system is influenced by iron. Goethite is a form of iron hydroxide, which is commonly found in sediments. In previous studies, we have used iron complexes to degrade organic pollutants. Results have shown that some organic pollutants could be totally degraded by iron complexes and our work indicated that iron might cause conversion of arsenic when irradiated. This work attempts to investigate the conversion of arsenite [As(III)] using natural goethite, as the iron source, to quantify the effect of various factors on photooxidation. We also consider the possible mechanism for photooxidation of As(III) using a suspension of natural goethite. The As(III) concentration variation under illumination was compared with the one in the dark to quantify the contribution of light to As(III) oxidation to As(V) in goethite suspended solution. The experiments under N₂ and air atmosphere confirmed the participation of dissolved oxygen. The photooxidation efficiency of As(III) under different conditions was compared to determine the effect of different environmental factors such as pH value, goethite concentration, and humic acid concentration on the photooxidation reaction. In the solution containing 100 μg L⁻¹ arsenite and 0.1 g L⁻¹ suspended goethite at pH 3.0, nearly 80 % of As(III) was photooxidized after irradiation by a 250-W metal halogen lamp (λ ≥ 313 nm) after 6 h. The effects of initial pH and goethite concentration and humic acid concentration were all examined. The results show that the greatest efficiency of photooxidation of As(III) was at pH 3.0. The extent of photooxidation decreased with increasing goethite concentration and fell sharply in the presence of humic acid under the conditions in this work. Although about 80 % of As(III) was photooxidized after irradiation by a 250-W halogen lamp at pH 3.0 in the presence of goethite suspension, photooxidation was also affected by factors such as pH, concentration of goethite, and presence of humic acid. The scavenger experiments showed that the HO• radical and photogenerated hole are the predominant oxidants in this system responsible for 87.1 % oxidation of As(III), while HO ₂ • /O ₂ •⁻ is responsible for 12.9 % oxidation of As(III).

Hyperaccumulators contain tubular cellulose and heavy metals, which can be used as the sources of carbon and metals to synthesize nanomaterials. In this paper, carbon nanotubes (CNTs), Cu₀.₀₅Zn₀.₉₅O nanoparticles, and CNTs/Cu₀.₀₅Zn₀.₉₅O nanocomposites were synthesized using Brassica juncea L. plants, and the ultraviolet (UV)-light-driven photocatalytic degradations of bisphenol A (BPA) using them as photocatalysts were studied. It was found that the outer diameter of CNTs was around 50 nm and there were a few defects in the crystal lattice. The synthesized Cu₀.₀₅Zn₀.₉₅O nanocomposites had a diameter of around 40 nm. Cu₀.₀₅Zn₀.₉₅O nanocomposites have grown on the surface of the CNTs and the outer diameter of them was around 100 nm. The synthesized hybrid carbon nanotubes using B. juncea could enhance the efficiency of photocatalytic degradation on BPA. The complete equilibration time of adsorption/desorption of BPA onto the surface of CNTs, Cu₀.₀₅Zn₀.₉₅O nanoparticles, and CNTs/Cu₀.₀₅Zn₀.₉₅O nanocomposites was within 30, 20, and 30 min, and approximately 14.9, 8.7, and 17.4 % BPA was adsorbed by them, respectively. The combination of UV light irradiation (90 min) with CNTs, Cu₀.₀₅Zn₀.₉₅O nanoparticles, and CNTs/Cu₀.₀₅Zn₀.₉₅O nanocomposites could lead to 48.3, 75.7, and 92.6 % decomposition yields of BPA, respectively. These findings constitute a new insight for synthesizing nanocatalyst by reusing hyperaccumulators.

Wastewater released from textile industries causes water pollution, and it needs to be treated before discharge to the environment by cost effective technologies. Solar photocatalysis is a promising technology for the treatment of dye wastewater. The Ag@TiO nanoparticles comprising of Ag core and TiO shell (Ag@TiO) have unique photocatalytic property of inhibition of electron-hole recombination and visible light absorption, which makes it a promising photocatalyst for use in solar photocatalysis and with higher photocatalytic rate. Therefore, in the present work, the Ag@TiO nanoparticles synthesized by one pot method with postcalcination step has been used for the degradation of Acid Yellow-17 (AY-17) dye under solar light irradiation. The Ag@TiO nanoparticles were characterized using thermogravimetric-differential thermal analysis, X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray analysis. The catalyst has been found to be very effective in solar photocatalysis of AY-17, as compared to other catalysts. The effects of pH, catalyst loading, initial dye concentration, and oxidants on photocatalysis were also studied. The optimized parameters for degradation of AY-17 using Ag@TiO were found to be pH 3, dye/catalyst ratio of 1:10 (g/g), and 2 g/L of (NH)SO as oxidant. Efficient decolorization and mineralization of AY-17 was achieved. The kinetics of color, total organic carbon, and chemical oxygen demand removal followed the Langmuir-Hinshelwood model. Ag@TiO catalyst can be reused thrice without much decline in efficiency. The catalyst exhibited its potential as economic photocatalyst for treatment of dye wastewater.

This paper demonstrated the relative bactericidal activity of photoirradiated (6W-UV Torch, λ > 340 nm and intensity = 0.64 mW/cm) P25-TiO nanoparticles, nanorods, and nanotubes for the killing of Gram-negative bacterium Agrobacterium tumefaciens LBA4404 for the first time. TiO nanorod (anatase) with length of 70-100 nm and diameter of 10-12 nm, and TiO nanotube with length of 90-110 nm and diameter of 9-11 nm were prepared from P-25 Degussa TiO (size, 30-50 nm) by hydrothermal method and compared their biocidal activity both in aqueous slurry and thin films. The mode of bacterial cell decomposition was analyzed through transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR), and K ion leakage. The antimicrobial activity of photoirradiated TiO of different shapes was found to be in the order P25-TiO > nanorod > nanotube which is reverse to their specific surface area as 54 < 79 < 176 m g, evidencing that the highest activity of P25-TiO nanoparticles is not due to surface area as their crystal structure and surface morphology are entirely different. TiO thin films always exhibited less photoactivity as compared to its aqueous suspension under similar conditions of cell viability test. The changes in the bacterial surface morphology by UV-irradiated P25-TiO nanoparticles was examined by TEM, oxidative degradation of cell components such as proteins, carbohydrates, phospholipids, nucleic acids by FT-IR spectral analysis, and K ion leakage (2.5 ppm as compared to 0.4 ppm for control culture) as a measure of loss in cell membrane permeability.

The ubiquitous dissolved organic matter (DOM) has an important influence on transformation of organic contaminants through the production of reactive substances, such as •OH, ¹O₂, and ³DOM*. The photolysis of a higher chlorinated polychlorinated biphenyl (PCB) congener (2,2′,4,4′,5,5′-hexachlorobiphenyl, PCB 153) under simulated sunlight in presence of humic acid (HA) was investigated. Degradation of PCB 153 was accelerated significantly by the addition of HA, with a rate constant of 0.0214, 0.0413, and 0.0358 h⁻¹ in the initial 18 h of irradiation in presence of 1, 5, and 20 mg/L HA, respectively. The main photodegradation products analyzed by gas chromatography mass spectrometry were 4-hydroxy-2,2′,4′,5,5′-pentaCB and 2,4,5-trichlorobenzoic acid. Main reactive species involved were determined by the electron spin-resonance spectroscopy, including ¹O₂ and •OH. Special scavengers were added to elucidate the photolysis mechanisms. By using the specific scavengers, it turned out that •OH accounted for 29.3 % of the degradation, and the intra-DOM reactive species (¹O₂, •OH, and ³DOM*) accounted for 59.6 % of the degradation. Photo-transformation sensitized by DOM, which involves both aqueous and intra-DOM reactions of PCBs with reactive species, may be one of the most important mechanisms for natural attenuation of PCBs.

In the present study, the photocatalytic degradation of Reactive Red 195 (RR195) from aqueous samples under UV-A irradiation by using anatase/brookite TiO₂ (A/B TiO₂) mesoporous nanoparticles has been investigated. Batch experiments were conducted to study the effects of the main parameters affecting the photocatalytic process. The effects and interactions of most influenced parameters, such as substrate concentration and catalyst load, were evaluated and optimized by using a central composite design model and a response surface methodology. The results indicated that the dye degradation efficiency in the experimental domain investigated was mainly affected by the tested variables, as well as their interaction effects. Analysis of variance showed a high coefficient of determination value (R ² = 0.9947), thus ensuring a satisfactory adjustment of the first-order regression model (2FI model) with the experimental data. The obtained results also indicate that catalyst loading plays an important role in determining the removal efficiency of RR195 attributable to both photodegradation and adsorption process. Under optimal conditions (initial dye concentration (50 mg/L) and catalyst loading (2,000 mg/L), A/B TiO₂ showed similar removal efficiency compared to that of commercial titania (Degussa P25). Also, at these conditions, complete degradation of RR195 can be achieved by both catalysts within 15 min under UV-A irradiation. The experiments demonstrated that dye removal on the prepared A/B TiO₂ was facilitated by the synergistic effects between adsorption and photocatalysis. Photocatalytic mineralization of RR195 was monitored by total organic carbon. The recycling experiments confirmed the stability of the catalyst.