Construction of triphase interface for catalytic ozonation of polluted water.

The utilization efficiency of ozone determines the cost of catalytic ozonation in water treatment. Herein, a triphase catalytic system was constructed by aerating ozone through a CeO2 loaded Al2O3 ceramic membrane (CeO2-CM) for disinfection and antibiotic degradation. Ozone aeration and a packed catalyst system (CeO2-Packing) were set as the controls. Results showed that CeO2-CM reduced the ozone escape by 34.6%-56.2%. The ozone utilization capacity of CeO2-CM for E. coli inactivation was 33.1% and 33.8% higher than those of CeO2-Packing and ozone aeration, respectively. The ozone utilization capacity of CeO2-CM for sulfamethoxazole degradation was 88.5% and 183.1% higher than those of CeO2-Packing and ozone aeration, respectively. CeO2-CM, with the lowest ozone escape and highest ozone utilization efficiency, significantly enhanced the performance of catalytic ozonation in disinfection and antibiotic degradation. This work proposes a feasible strategy for minimizing ozone consumption in water treatment.

Optimization of Co3O4 surface sites for photo-ozone catalytic mineralization of dichloromethane.

Obtaining high removal rate of chlorinated volatile organic compounds (CVOCs) and CO2 selectivity with a low ratio of O3/CVOC and energy consumption is challenging. Dodecylamine was used in this study to create active sites on Co3O4 for photo-ozone catalytic mineralization of dichloromethane (DCM). Amine-Co3O4-450 is a dodecylamine-modified sample with high density of Co3+, Co2+, and hydroxyl due to its nanosheet structure and exposed (112) facets. The optimized surface significantly enhanced the cleavage of the C-Cl bond at low temperatures. Photocatalysis primarily participated in the oxidation of intermediates following DCM dichlorination and significantly improved CO2 selectivity. The respective DCM removal rate and mineralization efficiency of Amine-Co3O4-450 with an O3/DCM molar ratio of 1.27 and one-sun irradiation were 14.9 and 15.0 times higher than the sum of those in the presence of light irradiation or O3 alone. This finding indicated that a strong synergistic effect exists between O3 and light.

Effect of photothermal conversion on ozone uptake over deposited mineral dust.

The deposited dust provides a large surface for heterogeneous ozone uptake reactions in urban regions. Prior studies have barely considered the effect of the photothermal conversion of deposited dust and underlying surface on ozone uptake. In this study, Fe2O3, TiO2, α-Al2O3, and SiO2 were selected as model mineral dusts (MDs) to evaluate the photothermal effect. With an irradiation intensity of 100 mW/cm2, the uptake coefficients of ozone by Fe2O3, TiO2, α-Al2O3, and SiO2 were 2.4, 30, 2.72, and 2.83 times higher than those in a dark condition. For SiO2 and α-Al2O3, the increase in the uptake coefficient was due to the temperature increase induced by photothermal conversion. For Fe2O3 and TiO2, photoelectric and photothermal conversion simultaneously participated in ozone uptake reactions. At 70 °C, the contribution of thermal catalysis to ozone uptake over Fe2O3 and TiO2 was approximately 55.4 % and 55.0 %, respectively. The temperature increase induced by photothermal conversion also promoted MDs' activity for ozone uptake after removing the light source (after sunset). This work proves that the ozone uptake induced by the photothermal effect of deposited MDs and the underlying surface was the primary ozone elimination pathway in urban atmospheres.

Optimization of photothermal conversion and catalytic sites for photo-assisted-catalytic degradation of volatile organic compounds.

Solar energy conversion is a promising strategy to enhance the elimination of volatile organic compounds (VOCs) and minimize power consumption. Herein, non-noble metal WC@WO3 as cocatalyst was composited with CeO2 to optimize photochemical and photothermal conversion for the catalytic ozonation of toluene and acetone. The photothermal conversion efficiencies of visible and infrared lights on 20%WC@WO3-CeO2 were 2.2 and 10.4 times higher than those on CeO2, respectively, which indicates that the equilibrium temperature of the catalyst remarkably increased under full-spectrum light irradiation. Moreover, WC@WO3 transferred electrons to CeO2 in 20%WC@WO3-CeO2 and thus remarkably improved the activity of catalytic sites. The synergy factor of light and O3 on 20%WC@WO3-CeO2 was 5.8, and the reaction rate of toluene and acetone reached 9274.5 and 35779.0 mg/(m3∙min), respectively. This work provides a low-cost and high-efficient catalyst for the utilization of solar energy for VOC control.

Metallic oxide nanomaterials act as antioxidant nanozymes in higher plants: Trends, meta-analysis, and prospect.

Improving plant resistance against various environmental stresses is crucial to gain higher agricultural productivity for meeting future food demands of the fast-growing global population. Nanozymes, nanomaterials (NMs) with enzyme-like activity, have shown the potential to defend environmental stresses via scavenging reactive oxygen species (ROS) and augmenting the inherent antioxidant functions of plants. However, several studies confirmed that NMs could cause oxidative damage triggered by excessive ROS. In this study, the conversion mechanism between antioxidant and oxidant activities of metallic oxidative nanozymes was systematically reviewed and evaluated using meta-analysis approach. Moreover, our work attempts to seek the optimal dose and physicochemical property of antioxidant-functionalized NMs and put forward future research directions. The meta-analysis results indicated that NMs at a low dose (below 20 ppm) exhibited antioxidant activity which could scavenge ROS and alleviate their deleterious impacts. Conversely, their oxidant activity was activated at the exposure dose above 200 ppm which might induce ROS overproduction and lead to oxidative stress. Further, root exposure tends to stimulate the oxidant activity of NMs, and the NMs modification is highly promising for improving their bioavailability. A SWOT analysis was conducted to evaluate the strengths, weaknesses, opportunities, and threats of agro-applied nanozymes. Therefore, the rational design and development of nanozymes for better antioxidant potential will be beneficial to their applications in agriculture.

Fluorescent g-C3N4 nanosheets enhanced photosynthetic efficiency in maize.

Nano-enabled agriculture becomes a new and rapidly evolving area of research, particularly, nanomaterials (NMs) with light-harvesting capacities for enhancing photosynthesis. However, mechanisms for the interactions between these NMs and plants are not fully understood. Herein, fluorescent and water-soluble graphitic carbon nitride (g-C3N4) nanosheets were prepared and used as artificial antenna to amplify light harvesting ability and enhance photosynthesis in maize. Upon root exposure to 10 mg·L-1 g-C3N4 nanosheets, the g-C3N4 can be taken up and distributed in leaves. Also, the nutrients (Mg, P, Fe, and Mn), chlorophyll content, electron transfer rate, net photosynthetic rate, and carbohydrates content in maize were increased significantly by 1.1%, 51.8%, 44.6%, 121.8%, 12.1%, 44.5%, 30.0% and 32.3%, respectively. In addition, the gene expressions of psbA (photosystem II reaction center protein A) and psaA (photosystem I P700 chlorophyll A apoprotein A1) were up-regulated by 56.3% and 26.8%, respectively. Moreover, the activities of phosphoenolpyruvate carboxylase (PEPC) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were significantly increased by 242.3% and 156.3%, respectively. This study provides a new perspective on the use of g-C3N4 nanosheets to promote plant growth and develop nano-enabled agricultural technology.

Meta-cresol degradation by persulfate through UV/O3 synergistic activation: Contribution of free radicals and degradation pathway.

The kinetic and pathway of meta-cresol (m-cresol) degradation were studied by persulfate oxidation through UV/ozone activation (UV/O3-Na2S2O8) to improve m-cresol removal to eliminate ecological risks. Experimental results showed that the degradation effect of m-cresol with an initial concentration of 50 mg/L was 99.8% in 30 min under the optimization conditions. The reaction kinetic model in the UV/O3-Na2S2O8 system shows that the initial pH value, the respective ozone, and the persulfate dosage were positively correlated with the degradation rate constant value (k). The apparent degradation rate of m-cresol in the UV/O3-Na2S2O8 system was 0.2216 min-1, and the synergy factor (f) was larger than 1, thereby demonstrating a synergistic effect of UV, ozone, and persulfate. The dominant free radicals in the system were sulfate radical (SO- 4·) and hydroxyl radical (·OH), and the contribution ratio of SO- 4· to m-cresol degradation was higher than ·OH. The degradation process of m-cresol by UV/O3 - Na2S2O8 was mainly through the electrophilic addition reaction to substitute the ortho- and para-positions of the hydroxyl group on the benzene ring, followed by the ring-opening reaction and mineralization of the aliphatic compound to achieve the complete degradation of m-cresol.

Highly Dispersed and Small-Sized Nickel(II) Hydroxide Co-Catalyst Prepared by Photodeposition for Hydrogen Production.

Photodeposition has been widely used as a mild and efficient synthetic method to deposit co-catalysts. It is also worth studying how to synthesize non-noble metal photocatalysts with uniform dispersion. Different synthetic conditions in photodeposition have a certain influence on particle size distribution and photocatalytic activity. Therefore, we designed experiments to prepare the inexpensive composite photocatalyst Ni(OH)2 /g-C3 N4 by photodeposition. The Ni(OH)2 co-catalysts disperse uniformly with particle sizes of about 10 nm. The photocatalytic hydrogen production rate of Ni(OH)2 /g-C3 N4 reached about 19 mmol g-1 h-1 , with the Ni(OH)2 deposition amount about 1.57 %. During 16 h stability testing, the rate of hydrogen production did not decrease significantly. The composite catalyst also revealed a good hydrogen production performance under sunlight. The Ni(OH)2 co-catalyst enhanced the separation ability of photogenerated carriers, which was proved by surface photovoltage and fluorescence analysis.

Platinum-enhanced amorphous TiO2-filled mesoporous TiO2 crystals for the photocatalytic mineralization of tetracycline hydrochloride.

The adsorption ability and photoactivity of a photocatalyst largely determine the mineralization efficiency of antibiotics. Herein, aiming to enhance the adsorption and mineralization of antibiotics, we constructed a hierarchical porous core-shell structure by filling amorphous TiO2 in the pores of Pt-doped mesoporous TiO2 crystals (MCs). The physical-chemical properties of the prepared samples were investigated by surface photovoltage spectroscopy, X-ray photoelectron spectroscope, etc. Adsorption and photocatalysis experiments were conducted with tetracycline hydrochloride as the model antibiotic. Pt nanoparticles doped at the interface of the rutile-amorphous homojunction remarkably enhanced the built-in electric field. The enhanced electric field increased the hole transfer to the catalyst surface, and the Pt doping treatment promoted the growth of amorphous TiO2 into the mesopores of the MCs. The optimization increased the surface area of the catalyst without increasing the thickness of the amorphous TiO2 shell, thereby reducing the charge migration distance from the core-shell interface to the catalyst surface. The adsorption amount and mineralization efficiency of tetracycline hydrochloride for the porous core-shell composite were 6.7 and 3.8 times of those for MCs, respectively.

Localization and Stabilization of Photogenerated Electrons at TiO2 Nanoparticle Surface by Oxygen at Ambient Temperature.

Understanding the mechanism by which oxygen adsorption influences the separation behavior of charge carriers is important in photocatalytic removal of air pollutants. In this study, we performed steady-state surface photovoltage and surface photocurrent spectroscopy combined with an atmosphere control system to determine the effect of oxygen on the charge separation behavior at the surface of anatase TiO2 nanoparticles at ambient temperature. Results showed that photogenerated electrons were movable in N2 atmosphere but were localized in O2 atmosphere. O2 obviously enhanced the stabilization of the localized photogenerated electrons when the surface defects of TiO2 were fully occupied by adsorbed O2. Moreover, O2 adsorption increased the energy demand for exciting electrons from the valence band to localized surface defect states and reduced the density of band tail states. These findings suggest us that the effect of gaseous species on the mobility and stability of charge carriers should be considered to understand the photocatalytic degradation of air pollutants.

Crystallization of microporous TiO2 through photochemical deposition of Pt for photocatalytic degradation of volatile organic compounds.

The photocatalytic mineralization efficiency of volatile organic compounds (VOCs) is determined by adsorption of reactants, separation of charge carriers, and reaction activity of catalyst surface. Herein, we provide a strategy to synthesize a novel catalyst, namely, PhPt-Micro, which is characterized by high adsorption ability, charge separation efficiency, and surface reaction activity. Toluene was chosen as the model VOC. The effects of photochemical deposition of Pt on the physical properties of microporous amorphous TiO2 (Micro) and toluene mineralization were studied using N2 adsorption/desorption, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, GC-flame ionization detection, and surface photovoltage spectroscopy (SPS) analyses. After photochemical treatment, the structure of Micro was optimized, and Pt nanoparticles were successfully deposited at the outlet of electrons on the catalyst surface. SPS result proved that the optimized structure enhanced the separation efficiency of charge carriers and the migration of photo-generated electrons to the PhPt-Micro surface. The quasi-equilibrium adsorption amount of toluene over PhPt-Micro was two times higher than that with commercial nano TiO2 (P25). The micropores concentrated toluene on the catalyst surface and hindered intermediate desorption. The mineralization efficiency of toluene over PhPt-Micro was 2.4 and 5.9 times higher than those over Micro and P25, respectively.

Analytical Approaches for Determining Chemical Oxygen Demand in Water Bodies: A Review.

Chemical oxygen demand (COD) is a critical analytical parameter for water quality assessment. COD represents the degree of organic pollution in water bodies. However, the standard analytical methods for COD are time-consuming and possess low oxidation efficiency, chloride interference, and severe secondary pollution. Works performed during the last two decades have resulted in several technologies, including modified standard methods (e.g., microwave-assisted method) and new technologies or methods (e.g., electro- and photo-oxidative methods based on advanced oxidation processes) that are less time-consuming, environment friendly, and more reliable. This review is devoted in analyzing the technical features of the principal methods described in the literature to compare their performances (i.e., measuring window, reliability, and robustness) and identify the advantages and disadvantages of each method.