Microbial community response reveals underlying mechanism of industrial-scale manganese sand biofilters used for the simultaneous removal of iron, manganese and ammonia from groundwater.

Most studies have employed aeration-biofiltration process for the simultaneous removal of iron, manganese and ammonia in groundwater. However, what's inside the "black box", i.e., the potential contribution of functional microorganisms behavior and interactions have seldom been investigated. Moreover, little attention has been paid to the correlations between environmental variables and functional microorganisms. In this study, the performance of industrial-scale biofilters for the contaminated groundwater treatment was studied. The effluent were all far below the permitted concentration level in the current drinking water standard. Pyrosequencing illustrated that shifts in microbial community structure were observed in the microbial samples from different depths of filter. Microbial networks showed that the microbial community structure in the middle- and deep-layer samples was similar, in which a wide range of manganese-oxidizing bacteria was identified. By contrast, canonical correlation analysis showed that the bacteria capable of ammonia-oxidizing and nitrification was enriched in the upper-layer, i.e., Propionibacterium, Nitrosomonas, Nitrosomonas and Candidatus Nitrotoga. The stable biofilm on the biofilter media, created by certain microorganisms from the groundwater microflora, played a crucial role in the simultaneous removal of the three pollutants.

Publisher Correction: Microbial network of the carbonate precipitation process induced by microbial consortia and the potential application to crack healing in concrete.

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Microbial network of the carbonate precipitation process induced by microbial consortia and the potential application to crack healing in concrete.

Current studies have employed various pure-cultures for improving concrete durability based on microbially induced carbonate precipitation (MICP). However, there have been very few reports concerned with microbial consortia, which could perform more complex tasks and be more robust in their resistance to environmental fluctuations. In this study, we constructed three microbial consortia that are capable of MICP under aerobic (AE), anaerobic (AN) and facultative anaerobic (FA) conditions. The results showed that AE consortia showed more positive effects on inorganic carbon conversion than AN and FA consortia. Pyrosequencing analysis showed that clear distinctions appeared in the community structure between different microbial consortia systems. Further investigation on microbial community networks revealed that the species in the three microbial consortia built thorough energetic and metabolic interaction networks regarding MICP, nitrate-reduction, bacterial endospores and fermentation communities. Crack-healing experiments showed that the selected cracks of the three consortia-based concrete specimens were almost completely healed in 28 days, which was consistent with the studies using pure cultures. Although the economic advantage might not be clear yet, this study highlights the potential implementation of microbial consortia on crack healing in concrete.

Discussion on Local Spark Sintering of a Ceramic-Metal System in an SR-CT Experiment during Microwave Processing.

In this paper, local spark sintering of a ceramic-metal system (SiO2-Sn) during microwave processing was examinedby means of synchrotron-radiation-computed tomography technology. From the reconstructed 3-D and cross-section images of the specimen, adensification process was observed below the melting point of Sn, and then the specimen came into a rapid densification stage. These results may be due to the local spark sintering induced by the high-frequency alternating microwave electric fields. As the metallic particles Sn were introduced, the microstructure of "ceramic-metal" will lead to a non-uniform distribution and micro-focusing effect from electric fields in some regions (e.g., the neck). This will result in high-intensity electric fields and then induce rapid spark sintering within the micro-region. However, in the subsequent stage, the densification rate declined even when the specimen was not dense enough. The explanation for this is that as the liquid Sn permeated the gaps between SiO2, the specimen became dense and the micro-focusing effect of electric fields decreased. This may result in the decrease or disappearance of spark sintering. These results will contribute to the understanding of microwave sintering mechanisms and the improvement of microwave processing methods.

Modification Strategies with Inorganic Acids for Efficient Photocatalysts by Promoting the Adsorption of O2.

Efficient photocatalysis for degrading environmental organic pollutants on semiconductors requires photogenerated charge carrier separation to drive the photochemical processes. To ensure charge separation, it is indispensable to make charges captured effectively. Generally, the step for capturing the photogenerated electrons by the surface adsorbed O2 is relatively slow as compared to that for capturing holes by the surface adsorbed hydroxyl groups so that it is taken as the rate-determining step. However, it is frequently neglected. Thus, it is greatly desired to develop feasible strategies to promote the adsorption of O2 for efficient photocatalysts. In this paper, we have mainly discussed surface modification with inorganic acids, such as H3PO4, HF, and H3BO3, to enhance photogenerated charge carrier separation based on oxygen adsorption promotion for photocatalytic degradation of environmental pollutants. Among these acids, the function and mechanism of H3PO4 are highlighted because of its good performance and universality. Several important photocatalyst systems, mainly including TiO2, α-Fe2O3, and g-C3N4, along with the nanostructured carbons as electron acceptors in nanocomposites, are addressed to improve the ability to adsorb O2. A key consideration in this review is the development of a strategy for the promotion of adsorbed O2 for efficient photocatalysts, along with the process mechanisms by revealing the relationships among the adsorbed O2, photogenerated charge carrier separation, and photocatalytic performance. Interestingly, it is suggested that the enrichment in surface acidity be favorable for promotion of O2 adsorption, leading to the improved charge carrier separation and then to the enhanced photoactivities of various semiconductor photocatalysts. Moreover, several outlooks are put forward.

Enhanced photocatalytic activity of Cl-residual rutile TiO2 nanorods after targeted co-modification with phosphoric and boric acids.

The promotion of O2 adsorption on semiconductor surfaces for effectively capturing photogenerated electrons in the photocatalytic degradation of pollutants is highly desired. In this study, the targeted co-modification of residual chlorine rutile TiO2 nanorods with phosphoric and boric acids has been accomplished for the first time by simple wet chemical processes. The key to targeted co-modification is to connect -P-OH and -B-OH to the Cl-residual TiO2 surfaces by -Ti-OH and -Ti-Cl, respectively, consequently forming -Ti-O-P-OH and -Ti-Cl:B-OH ends. By means of the atmosphere-controlled surface photovoltage spectroscopy, the degrees for capturing photogenerated electrons by the adsorbed O2 as receptors on the resulting TiO2 nanorods are quantitatively analyzed. It is confirmed that the targeted co-modification could greatly promote the capture of the photogenerated electrons compared to the phosphate and borate modification alone. This is attributed to increased amounts of adsorbed O2 based on electrochemical O2 reduction and O2 temperature-programmed desorption measurements, further leading to the enhanced separation of photogenerated charges, characterized by an increase in the amount of produced hydroxyl radicals. This is responsible for the obviously enhanced photocatalytic activity of TiO2 nanorods towards the degradation of colorless gas-phase acetaldehyde and liquid-phase phenol. This work would provide us a feasible route for the co-modification with inorganic acids to synthesize efficient nanosized TiO2-based photocatalysts.

Phosphate-modified graphitic C3N4 as efficient photocatalyst for degrading colorless pollutants by promoting O2 adsorption.

The photocatalytic activity for degrading gas-phase acetaldehyde and liquid-phase phenol by graphitic carbon nitride could be greatly improved after modification with phosphoric acid, which is attributed to the clear increase in adsorbed O2 which prolongs the lifetime and enhances the separation of photogenerated charge carriers. This is based on O2 temperature-programmed desorption curves, steady-state surface photovoltage spectra, and time-resolved surface photovoltage responses.

Effects of Inorganic Acid Modification on Photocatalytic Performance of TiO2 and Its Activity-Enhanced Mechanism Related to Adsorbed O2.

In this work, commercial P25 TiO2 is modulated by post-treatments with different acidic substances, and the effects of residual acidic substances on the photogenerated charge separation of TiO2 and its photocatalytic activity are investigated in detail. It is demonstrated by means of atmosphere-controlled surface photovoltage spectroscopy that an increase in acid surface modification is favorable for improving the photogenerated charge separation of TiO2 . As a result, its photocatalytic activity for the degradation of gas-phase acetaldehyde is enhanced greatly. On the basis of measurements of O2 temperature-programmed desorption of untreated and treated TiO2 , it is confirmed that an increased amount of acid surface modification promotes the adsorption of O2 on TiO2 . Hence, it is suggested for the first time that an increase in surface acidity through post-treatment with an appropriate amount of acidic substance leads to a clear enhancement of the photocatalytic activity of TiO2 by promoting O2 adsorption, and thus, improving the photogenerated charge separation of TiO2 . This work provides a feasible route for the synthesis of high-activity oxide-based semiconductor photocatalysts through surface modification with stable inorganic acids.

Facile Synthesis of Phosphate-Functionalized MWCNT-TiO2 Nanocomposites as Efficient Photocatalysts and Insights into the Roles of Nanostructured Carbon.

Effectively contacted multiwalled carbon nanotube (MWCNT)-titanium dioxide nanocomposites and phosphate-functionalized MWCNT-TiO2 composites have been successfully synthesized by simple one-pot phase-separated hydrolysis-solvothermal processes. The key to this synthetic strategy is to disperse MWCNTs uniformly in Ti(OBu)4 in advance and then to put them into the toluene organic phase. The as-prepared nanocomposites between TiO2 and the correct amount of MWCNT exhibits higher activity in the photocatalytic degradation of rhodamine B than that with the resulting TiO2 , although the activity in the photocatalytic degradation of gas-phase aldehyde and liquid-phase phenol is lower. Interestingly, the functionalization of MWCNTs with an appropriate amount of phosphoric acids prior to the synthesis could greatly improve the activity of the MWCNT-TiO2 nanocomposites for the degradation of aldehyde and phenol, even superior to that of commercial P25 TiO2 . Based on the measurements of atmosphere-controlled surface photovoltage spectra and O2 temperature-programmed desorption, it is suggested that MWCNTs are favorable to increase rhodamine B adsorption on the composite to promote the photosensitization oxidation reactions, whereas it is unfavorable for the adsorption of O2 and responsible for the low photocatalytic activity for the degradation of colorless pollutants. Phosphate functionalization greatly enhances the amount of O2 adsorbed on the MWCNT, which leads to significant charge separation, and thus, to significant photoactivity for the degradation of colored and colorless pollutants of the nanocomposites.

Facile fabrication of efficient AgBr-TiO2 nanoheterostructured photocatalyst for degrading pollutants and its photogenerated charge transfer mechanism.

A simple microemulsion-like chemical precipitation method has been successfully developed to construct effectively-contacted AgBr-TiO(2) composite. The key of this method is the dual roles of Br(-) in the synthetic process, as linkers between cetyltrimethyl ammonium cation surfactants and nanocrystalline anatase TiO(2) in the acidic condition, and as bromine sources to directly produce nanocrystalline AgBr on the surfaces of TiO(2) by chemical precipitation. It is well demonstrated that the as-constructed AgBr-TiO(2) nanoheterostructured composites display effective photogenerated charge transfer between AgBr and TiO(2), favorable to improve charge separation, by means of the surface photovoltage technique in different atmospheres at the aid of outer electric fields, especially for the transient surface photovoltage technique in air. And also, the Br(-) in crystal lattice of AgBr could effectively capture photogenerated holes under illumination. These factors are well responsible for the enhanced activity for photocatalytic degradation of liquid phase aqueous phenol solution and gas phase acetaldehyde under either UV-visible or visible irradiation, and the stability of AgBr in the photocatalytic processes.

Enhanced photocatalytic activity of nc-TiO2 by promoting photogenerated electrons captured by the adsorbed oxygen.

Nanocrystalline TiO2 (nc-TiO2) was modified by a simple post treatment with monometallic sodium orthophosphate solution. It is shown that the surface modification with an appropriate amount of phosphate obviously enhances the surface photovoltage responses of nc-TiO2 in the presence of O2, clearly indicating that the separation of photogenerated charges is greatly improved by promoting the photoelectrons captured by the adsorbed O2. This is well responsible for its much high photocatalytic activity for degrading representative gas-phase acetaldehyde, liquid-phase phenol and rhodamine B of phosphate-modified nc-TiO2, compared with the unmodified nc-TiO2. Moreover, it is demonstrated that the amount of O2 adsorbed on the surfaces of nc-TiO2 is greatly increased after phosphate modification based on the O2 temperature programmed desorption curves, which is attributed to the substitution of -Ti-OH with -Ti-O-P-OH. It is suggested for the first time that the phosphate modification favors the O2 adsorbed on TiO2 so as to further promote the photogenerated electrons captured. This work would provide feasible routes to further improve the photocatalytic performance for degrading pollutants of oxide-based semiconductors.

Synthesis of efficient N-containing TiO2 photocatalysts with high anatase thermal stability and the effects of the nitrogen residue on the photoinduced charge separation.

Efficient N-containing TiO(2) nanoparticles with high anatase thermal stability were synthesized via a hexamethylenetetramine (HMT)-modified sol-hydrothermal process. The results showed that modification with proper amounts of HMT is effective in increasing the onset temperature of the phase transformation of TiO(2) from anatase to rutile. The enhancement of the anatase thermal stability of the modified TiO(2) was attributed to ammonia produced slowly by hydrolysis of the HMT molecules in the sol-hydrothermal process and, additionally, to the residual nitrogen species after the thermal treatment at high temperatures, as indicated by the XPS examination. Compared with the unmodified TiO(2), the modified TiO(2) obtained by a thermal treatment at high temperatures exhibited good photocatalytic performance under UV light and was found to even be superior to the commercially available P25-TiO(2). It was suggested that the residual N species (Ti-O-N), formed after the thermal treatment at high temperatures, along with the mixed phase composition, large surface area and the increase in the thermal stability, were responsible for the enhanced photocatalytic activity of modified TiO(2). It was demonstrated, by means of the surface photovoltage responses of the modified TiO(2) in different atmospheres along with the aid of an outer electric field, that the residual N species could effectively capture the photoinduced holes, which was favorable for the effective separation of the photoinduced charges. This work provides a feasible route to fabricate high-performance TiO(2)-based functional nanomaterials with high anatase thermal stability.