The effects of water, substrate, and intermediate adsorption on the photocatalytic decomposition of air pollutants over nano-TiO2 photocatalysts.

The photocatalytic performance of nano-TiO2 photocatalysts in air pollutant degradation greatly depends on the adsorption of water, substrates, and intermediates. Especially under excessive humidity, substrate concentration, and intermediate concentration, the competitive adsorption of water, substrates, and intermediates can seriously inhibit the photocatalytic performance. In the past few years, extensive studies have been performed to investigate the influence of humidity, substrate concentration, and intermediates on the photocatalytic performance of TiO2, and significant advances have been made in the area. However, to the best of our knowledge, there is no review focusing on the effects of water, substrate, and intermediate adsorption to date. A comprehensive understanding of their mechanisms is key to overcoming the limited application of nano-TiO2 photocatalysts in the photocatalytic decomposition of air pollutants. In this review, the progress in experimental and theoretical fields, including a recent combination of photocatalytic experiments and adsorption and photocatalytic simulations by density functional theory (DFT), to explore the impact of adsorption of various reaction components on nano-TiO2 photocatalysts is comprehensively summarized. Additionally, the mechanism and broad perspective of the impact of their adsorption on the photocatalytic activity of TiO2 in air treatment are also critically discussed. Finally, several solutions are proposed to resolve the current problems related to environmental factors. In general, this review contributes a comprehensive perspective of water, substrate, and intermediate adsorption toward boosting the photocatalytic application of TiO2 nanomaterials.

Facet-Dependent Competitive Adsorption Mechanisms of Chromate and Oxalic Acid on γ-FeO(OH) Nanocrystals.

Facet-dependent toxic metal adsorption of iron oxides widely occurred in natural environments. It is known that organic acids can alter the adsorption behaviors of trace elements by cooperative or competitive effects. However, the coadsorption mechanisms of the specific facets are still not fully understood. In the current investigation, Cr(VI) adsorption onto the lepidocrocite (γ-FeO(OH))-exposed facets in the presence of oxalic acid (OA) was studied using macroexperiments, in situ attenuated total reflectance Fourier transform infrared spectroscopy, X-ray adsorption fine structure, and density functional theory calculations. Rod-like lepidocrocite (R-LEP) with a high ratio of {001}/{010} facet showed excellent Cr(VI) adsorption capacity than that of plate-like lepidocrocite (P-LEP, the dominant facet is {010}) in the absence/presence of OA. Interestingly, OA reacted with R-LEP would be easier to diminish Cr(VI) adsorption than with P-LEP. The competitive adsorption occurred on the {001} facet due to the formation of inner-sphere OA configurations (monodentate mononuclear and bidentate mononuclear structures) and a bidentate binuclear Cr(VI) complex. However, OA coordinated with {010} facets via the outer-sphere complexes, while Cr(VI) could form a protonated monodentate binuclear configuration. These observations suggest that the competitive adsorption processes between OA and Cr(VI) exhibit facet dependence. Furthermore, lepidocrocite-exposed facets determine the interfacial interactions and geochemical behaviors of Cr(VI) in polluted environments.

Colorimetric assay for ultrasensitive detection of Ag(I) ions based on the formation of gold nanoparticle oligomers.

Here, we report an ultrasensitive colorimetric method for determination of Ag+ based on gold nanoparticle (AuNP) oligomers with dark-field microscopy. In a proof-of-concept trial, two cytosine-rich (C-rich) aptamers as the sensing elements and AuNPs as the transducer to produce the detectable signal are designed for Ag+ determination. Obviously, the C bases in the two aptamers play a crucial role in the coordination of highly specific C-Ag+-C. Through a specific C-Ag+-C coordination, one aptamer immobilized on the surface of AuNPs sitting on a glass slide hybridizes with the other aptamer in the solution, which triggers the formation of AuNP oligomers. The formation of plasmonic oligomers results in an obvious increase in the number of yellow and red spots in dark-field images, further leading to a significantly enhanced scattering intensity. By measuring the intensity change of AuNP oligomers in the dark-field images, the concentration of Ag+ can be readily determined. The limits of detection (LODs) of 0.246 pM and 0.388 pM in solution and river water sample were obtained, respectively. This ultrasensitive colorimetric approach could be extended to probe Hg2+ via T-Hg2+-T coordination in environmental samples.

Effect of biochar-derived DOM on contrasting redistribution of chromate during Schwertmannite dissolution and recrystallization.

Biochar-derived dissolved organic matter (BDOM), is extensively involved in the recrystallization of minerals and the speciation alteration of associated toxic metals. This study investigates how BDOM extracted from tobacco petiole (TP) or tobacco stalk (TS) biochar influences the speciation repartitioning of Cr(VI) in environments impacted by acid mine drainage (AMD), focusing on interactions with secondary minerals during Schwertmannite (Sch) dissolution and recrystallization. TP-BDOM, rich in lignin-like substances, slowed down the Cr-Sch dissolution and Cr release under acidic conditions compared to TS-BDOM. TP-BDOM's higher O/C component exerts a delayed impact on Cr-Sch stability and Cr(VI) reduction. In-situ ATR-FTIR and 2D-COS analysis showed that carboxylic and aromatic N-OH groups in BDOM could interact with Cr-Sch surfaces, affecting sulfate and Cr(VI) release. It was also observed that slight recrystallization occurred from Cr-Sch to goethite, along with increased Cr incorporation into secondary minerals within TS-BDOM. This enhances our understanding of BDOM's role in Cr(VI) speciation changes in AMD-contaminated sites.

Visible-light-driven peroxymonosulfate activation by robust TiO2-base nanoparticles for efficient removal of sulfamethoxazole.

In this study, a novel bimetallic Co-Mo-TiO2 nanomaterial was fabricated through a simple two-step method, and applied as photocatalyst to activate peroxymonosulfate (PMS) with high efficiency for sulfamethoxazole (SMX) removal under visible light. Nearly 100% of SMX was degraded within 30 min in Vis/Co-Mo-TiO2/PMS system, and its kinetic reaction rate constant (0.099 min-1) was 24.8 times higher compare with the Vis/TiO2/PMS system (0.014 min-1). Moreover, the quenching experiments and the electronic spin resonance analysis results confirmed that both 1O2 and SO4•- were the dominant active species in the optimal system, and the redox cycles of Co3+/Co2+ and Mo6+/Mo4+ promoted the generation of the radicals during the PMS activation process. Additionally, the Vis/Co-Mo-TiO2/PMS system exhibited a wide working pH range, superior catalytic performance toward different pollutants and excellent stability with 92.8% SMX removal capacity retention after three consecutive cycles. The result of density functional theory (DFT) suggested that Co-Mo-TiO2 exhibited a high affinity for PMS adsorption, as indicated by the length O-O bond from PMS and the Eads of the catalysts. Finally, the possible degradation pathway of SMX in optimal system was proposed through intermediate identification and DFT calculation, and a toxicity assessment of the by-products was also conducted.

Heavy metal content and microbial characteristics of soil plant system in Dabaoshan mining area, Guangdong Province.

The disordered mining of Dabaoshan lead-zinc mineral resources in Shaoguan has brought serious harm to the regional ecological environment. In order to investigate the heavy metal pollution status and microbial characteristics of soil plant system in mining area, The distribution of heavy metals in the soil, the activity of soil microorganisms and the accumulation characteristics of heavy metals in the dominant plant Miscanthus floridulus were studied. The results indicated that metal element contents of Miscanthus floridulus in sequence were: Zn>Pb>Cu> Cd. This study demonstrated that the elemental content of the Miscanthus floridulus plant showed Zn>Pb>Cu>Cd, with Zn being the most significantly correlated with soil elements, followed by Pb. Compared with the control group, the Miscanthus floridulus-soil system possessed obviously different soil microbial features: intensiver in microbial basal respiration strength, and higher microbial eco-physiological parameters Cmic/Corg and qCO2, but lower in soil microbial biomass. The results showed the soil enzymatic activities decreased significantly with increase of contamination of heavy metals, especially dehydrogenase and urease activities. With the increase of the content of heavy metals in the mining area soil, the intensity of soil biochemical action in the mining area (Q1, Q2) soil decreased significantly, and the biochemical action showed a significant negative correlation with the content of heavy metals in the soil. Compared with the non mining area (Q8) soil, the intensity of soil ammonification, nitrification, N fixation and cellulose decomposition decreased by 43.2%~71.1%, 70.1%~92.1%, 58.7%~87.8% and 55.3%~79.8% respectively. The decrease of soil microbial activity weakened the circulation rate and energy flow of C and N nutrients in the soil of the mining area.

Effect of fulvic acid co-precipitation on biosynthesis of Fe(III) hydroxysulfate and its adsorption of lead.

Iron (III) co-precipitation with dissolved organic matter (DOM) is pervasive in many natural environments. However, the effects of DOM on the formation of Fe(III) hydroxysulfate (FHS) and its environmental implications are poorly understood. In this study, fulvic acid (FA) was used as a model DOM compound, and experiments were devised to investigate the effects of FA on the formation of FHS. In addition, the Pb(II) adsorption capabilities of FHSs biosynthesized under various FA dosages, including kinetics and sorption isotherm experiments, were conducted. These experiments showed that co-precipitation of FA promoted the formation of Fe-FA composites, FA-doped schwertmannite, and small particles of jarosite. Co-precipitates are more enriched in carboxyl (-COOH) functional groups due to their preferential binding with FHS. The adsorption kinetics, isotherms and mechanisms of Pb onto the biosynthesized FHSs were then comprehensively characterized and modeled. Though the specific surface area decreased with increasing FA loading, the introduction of FA into FHSs increased Pb(II) adsorption, with the highest concentration of FA addition improving the removal capacity of Pb(II) to 91.54%. Kinetics studies and intra-particle diffusion models indicated that the adsorption of Pb(II) onto the FHSs was correlated with the number of active sites, and two adsorption steps: surface adsorption and the diffusion of Pb(II) in channels inside the biosynthesized FHSs, are suggested. The adsorption mechanism was attributed to cation exchange between Pb(II) and -OH and -COOH functional groups, and the co-precipitated FA provided additional sites for Pb(II) adsorption by FHS.

Effect of calcium addition in plasma catalysis for toluene removal by Ni/ZSM-5 : Acidity/basicity, catalytic activity and reaction mechanism.

The effect of Ca modification on the Ni/ZSM-5 catalyst for efficient toluene oxidation was studied in a plasma-catalytic system. The Ni/ZSM-5 and Ca-Ni/ZSM-5 catalysts were prepared by a wet impregnation method and characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Pyridine-FTIR spectroscopy and temperature programmed desorption of ammonia (NH3-TPD). Among the catalysts tested, the Ca-Ni/ZSM-5 sample showed the best potential for toluene conversion (90.2%) and CO2 selectivity (70.7%). Pyridine-FTIR spectra and NH3-TPD results proved that the introduction of Ca and Ni onto ZSM-5 caused a decrease in the strong and weak acidic sites. In addition, gas chromatography/mass spectrometry (GC-MS) result showed that the Ca-Ni/ZSM-5 catalyst reduced the production of undesirable byproducts (such as p-nitrotoluene and methyl benzoate). Calcium in the Ni/ZSM-5 system influenced the acidity and other surface characteristic of the catalyst, as well as directly impacting the reactive plasma species and the intermediates. Finally, possible reaction mechanisms in the plasma catalysis of toluene were also proposed.

Visible light photocatalytic degradation of tetracycline with porous Ag/graphite carbon nitride plasmonic composite: Degradation pathways and mechanism.

Ag/g-C3N4 plasmonic photocatalysts with porous structure (Ag/PCN) were successfully synthesized via a thermal exfoliation strategy and photo-reduction method. Owing to the combined merits of porous structure and surface plasmon resonance effect of silver nanoparticles, the Ag/PCN catalysts exhibited excellent photocatalytic performance for the degradation of antibiotic agents. With the optimal Ag loading, the Ag/PCN-2 catalyst exhibited the optimal catalytic activity for TC degradation under visible light, which shows about 11.8 times enhancement in the photocatalytic removal efficiency as compared to pure g-C3N4, respectively. This phenomenon can be attributed to the increased specific surface area, broadened visible light absorption and improved charge separation. The radical quenching results confirmed that h+ and O2- radicals were the major active species during removal of TC. The degradation of TC is increased with the increment of Ag/PCN-2 catalysts, and the optimum catalyst was found to be 1.67 g/L. The hindering effect of selected of anions (Cl-, CO3-, H2PO4-) was found to follow the order H2PO4- > CO3- > Cl-. Ag/PCN-2 sample also possessed high stability after six cycles of reuses. Furthermore, the possible degradation pathways of TC and photocatalytic mechanism over Ag/PCN-2 were proposed in detail.

Response of net primary productivity to vegetation restoration in Chinese Loess Plateau during 1986-2015.

Land use and land cover change induced by large scale ecological restoration programs has a significant impact on the terrestrial ecosystem carbon cycle, especially on the net primary productivity (NPP) in arid and semi-arid regions. This study investigated the change in NPP caused by the large-scale ecological restoration in the Chinese Loess Plateau (LPR) region from 1986 to 2015 based on land cover datasets and NPP calculated using the Carnegie-Ames-Stanford Approach model. The results indicated that the annual total NPP exhibited a significant uptrend (P < 0.01) throughout the whole vegetation restoration region during the last 30 years, with an annual increase of 0.137 Tg C. A significant abrupt change was detected in 2006 for the annual total NPP series. Over half of the restoration region showed an increase in NPP in the past three decades, however, about 30~40% of the vegetation restoration region exhibited NPP loss before 2006, but subsequently NPP loss was found in only approximately 20% of the study region. Overall, the increase in NPP attributed to the vegetation restoration reached 51.14 Tg C in the past three decades, indicating that these large-scale vegetation restoration programs increased the carbon sequestration capacity of terrestrial ecosystems in the Loess Plateau. The findings of this study improve our understanding of the effects of the green campaign on terrestrial ecosystems.

Photocatalytic Decomposition of Gaseous HCHO over Ag Modified TiO2 Nanosheets at Ambient Temperature.

Ag nanoparticles loaded onto TiO2 nanosheets with exposed {001} facets were synthesized by solvothermal hydrolysis and photoreduction deposition methods. The results suggested that Ag NPs were uniformly dispersed on the surface of anatase TiO2 NSs with a metallic state. The Raman scattering and visible light absorption performances of Ag/TiO2 NSs were enhanced by Ag NPs due to their surface plasmon resonance effect. Photocatalytic oxidation experiments for HCHO were carried out under visible light, and the enhanced photocatalytic activity of Ag/TiO2 NSs can be attributed to the synergistic effects of the following factors: (1) the {001} facets, which possessed higher surface energy, showed higher photocatalytic activity; (2) the Ag NPs, the increased oxygen vacancies, and O2 adsorption on {001} facets can trap photoelectrons, thus inhibiting the recombination of photoelectrons and holes; (3) the Ag NPs can extend the light response range of TiO2 into visible light. The in situ FTIR results showed that higher mineralization efficiency of HCHO was achieved on Ag/TiO2 NSs than on Ag/TiO2 NPs. Additionally, the mechanism for HCHO photocatalytic oxidation was also discussed.

Integral structured Co-Mn composite oxides grown on interconnected Ni foam for catalytic toluene oxidation.

Considering the three-dimensional ordered network of Ni foam-supported catalysts and the toxicity effects of volatile organic compounds (VOCs), the design of proper active materials for the highly efficient elimination of VOCs is of vital importance in the environmental field. In this study, a series of Co-Mn composite oxides with different Co/Mn molar ratios grown on interconnected Ni foam are prepared as monolithic catalysts for total toluene oxidation, in which Co1.5Mn1.5O4 with a molar ratio of 1 : 1 achieves the highest catalytic activity with complete toluene oxidation at 270 °C. The Co-Mn monolithic catalysts are characterized by XRD, SEM, TEM, H2-TPR and XPS. It is observed that a moderate ratio of Mn/Co plays significant effects on the textural properties and catalytic activities. From the XPS and H2-TPR characterization results, the obtained Co1.5Mn1.5O4 (Co/Mn = 1/1) favors the excellent low-temperature reducibility, high concentration of surface Mn3+ and Co3+ species, and rich surface oxygen vacancies, resulting in superior oxidation performance due to the formation of a solid solution between the Co and Mn species. It is deduced that the existence of the synergistic effect between Co and Mn species results in a redox reaction: Co3+-Mn3+ ↔ Co2+-Mn4+, and enhances the catalytic activity for total toluene oxidation.

Performance of Toluene Removal in a Nonthermal Plasma Catalysis System over Flake-Like HZSM-5 Zeolite with Tunable Pore Size and Evaluation of Its Byproducts.

In this study, a series of HZSM-5 catalysts were prepared by the chemical liquid-phase deposition method, and low concentration toluene degradation was carried out in an atmospheric pressure dielectric barrier discharge (DBD) reactor. The catalysts were characterized by X-ray powder diffraction (XRD), SEM, TEM, and N2 adsorption analysis techniques. In addition, several organic contaminants were used to evaluate the adsorption performance of the prepared catalysts, and the effect of pore size on the removal efficiency of toluene and byproduct formation was also investigated. The unmodified HZSM-5 zeolite (Z0) exhibited good performance in toluene removal and CO2 selectivity due to the diffusion resistance of ozone and the amounts of active species (OH• and O•). Meanwhile, the time of flight mass spectrometry (TOF-MS) result showed that there were more byproducts of the benzene ring in the gas phase under the action of small micropore size catalysts. Moreover, the surface byproducts were detected by gas chromatography⁻mass spectrometry (GC-MS).

[Characteristics of multi-scale temporal-spatial distribution of urban heat island in Guangzhou].

Hourly data were collected from 47 automatic weather stations in Guangzhou to calculate the Guangzhou urban heat island (UHI) intensity in January, April, July and October 2001. The Kriging interpolation showed that the spatial variation of Guangzhou UHI was closely correlated with underlying surface, man-made heat, atmospheric pollutant and weather system, and the analysis on the temporal variation from January 2001 to February 2002 by Morlet wavelet transform revealed that there were multi-scale UHI periods. The main time scales were daily, weekly and bimonthly periods, and the secondary time scale was trimestral period. Sea-land breeze, man-made heat, long wave radiation of earth surface, and heat exchanges on earth surface affected the daily period, human activities affected the weekly period, solar radiation and weather system affected the bimonthly, period, while monsoon affected the trimestral period. This temporal-spatial variation of Guangzhou urban heat island was deeply affected by the coactions of weather system, long wave radiation, underlying surface, atmospheric pollutant, man-made heat, and heat exchanges on earth surface, etc.

[Spatio-temporal change and gradient differentiation of landscape pattern in Guangzhou City during its urbanization].

Guangzhou City is a rapidly urbanizing city in China, and a constructed city with holistic planning. By using the remote sensing images of 1985, 1990, 1995, 2000 and 2004, this paper studied the 20 years spatio-temporal changes of landscape pattern in Guangzhou, and analyzed the relationships between these changes and urbanization. The landscape and class-level pattern indices of whole Guangzhou City and its five districts were compared, and the results indicated that the landscape pattern in Guangzhou had an obvious spatio-temporal variation, and an increase of diversity and fractal dimension. The landscape structural complexity and fragmentation increased gradually from 1985 to 2004, and the variation intensity and tendency varied during four comparative stages 1985-1990, 1990-1995, 1995-2000, and 2000-2004. It was a rapid development period from 1985 to 1995 in Guangzhou. The represents of ten districts varied in their spatio-temporal landscape pattern, because of the different development progress and planning motive. The urbanization of Panyu was from 1990 to 2000, and its natural landscape was seriously disturbed by human activities. The represents of Conghua and Zengcheng districts were of integrative disturbance, and also, the urbanization process mainly took place during 1990-2000. In the city center consisting of 8 official constructed districts, the urbanization process happened earlier. In Huadu district, the landscape change revealed the frequent and severe human disturbance.