A p-n Junction by Coupling Amine-Enriched Brookite-TiO2 Nanorods with CuxS Nanoparticles for Improved Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction is a promising technology for reaching the aim of "carbon peaking and carbon neutrality", and it is crucial to design efficient photocatalysts with a rational surface and interface tailoring. Considering that amine modification on the surface of the photocatalyst could offer a favorable impact on the adsorption and activation of CO2, in this work, amine-modified brookite TiO2 nanorods (NH2-B-TiO2) coupled with CuxS (NH2-B-TiO2-CuxS) were effectively fabricated via a facile refluxing method. The formation of a p-n junction at the interface between the NH2-B-TiO2 and the CuxS could facilitate the separation and transfer of photogenerated carriers. Consequently, under light irradiation for 4 h, when the CuxS content is 16%, the maximum performance for conversion of CO2 to CH4 reaches at a rate of 3.34 µmol g-1 h-1 in the NH2-B-TiO2-CuxS composite, which is approximately 4 times greater than that of pure NH2-B-TiO2. It is hoped that this work could deliver an approach to construct an amine-enriched p-n junction for efficient CO2 photoreduction.

Highly efficient Cr(VI) removal from industrial electroplating wastewater over Bi2S3 nanostructures prepared by dual sulfur-precursors: Insights on the promotion effect of sulfate ions.

In this work, different Bi2S3 nanostructures were prepared from various single and dual sulfide precursors via a solvothermal method. It was found that Bi2S3 nanostructures prepared from dual sulfur precursors of L-cysteine and ammonium sulfide exhibited highest Cr(VI) removal ability with maximum Cr(VI) removal capacity of 148.95 mg/g in Cr(VI) solution (pH = 2). More importantly, the removal capacity strikingly increased to 223.33 and 240.25 mg/g in two kinds of actual industrial electroplating wastewater. By analyzing the components of actual electroplating wastewater and the results of control experiments in the absence and presence of different ions in Cr(VI) solution, it was found that SO42- played a critical role in the Cr(VI) removal over Bi2S3. The addition of SO42- could promote the conversion of Cr(VI) to Cr(III) on the surface of Bi2S3, thus leading to the enhanced Cr(VI) removal ability in actual electroplating wastewater. The Bi2S3 maintained its original Cr(VI) removal ability after four cycles in the electroplating wastewater, indicating the moderate reuse ability of the sample. This work not only demonstrated an highly efficient nanomaterials for the Cr(VI) removal in industrial electroplating wastewater, but also provided an insight on the influence of the components in wastewater on Cr(VI) removal.

Integrated p-n/Schottky junctions for efficient photocatalytic hydrogen evolution upon Cu@TiO2-Cu2O ternary hybrids with steering charge transfer.

Solar-driven photocatalytic H2 evolution could tackle the issue of fossil fuels-triggered greenhouse gas emission with sustainable clean energy. However, splitting water into hydrogen with high performance by a single semiconductor is challenging because of the poor charge separation efficiency. Herein, a novel ternary Cu@TiO2-Cu2O hybrid photocatalyst with multiple charge transfer channels has been designed for efficient solar-to-hydrogen evolution. Indeed, the ternary Cu@TiO2-Cu2O hybrid by coupling Cu@TiO2 with Cu2O nanoparticles shows highly-efficient photocatalytic hydrogen generation with rate of 12000.6 µmol·g-1·h-1, which is 4.4, 2.1, and 1.9 times higher than the pure TiO2 (2728.8 µmol·g-1·h-1), binary Cu@TiO2 (5595.5 µmol·g-1·h-1), and TiO2-Cu2O (6076.8 µmol·g-1·h-1) composite, respectively. In such a Cu@TiO2-Cu2O hybrid, the formed internal electric field in the TiO2-Cu2O p-n junction allows the electrons in Cu2O to migrate to TiO2, while the electrons in the CB of TiO2 could flow into Cu via the Schottky junction at the Cu@TiO2 interface. In this regard, a multiple charge transfer is achieved between the Cu@TiO2 and Cu2O, which facilitates promoted charge separation and results in the construction of electron-accumulated center (Cu) and hole-enriched surface (Cu2O). This p-n/Schottky junctions with steered charge transfer assists the hydrogen production upon the Cu@TiO2-Cu2O ternary photocatalyst.

Co-embedding oxygen vacancy and copper particles into titanium-based oxides (TiO2, BaTiO3, and SrTiO3) nanoassembly for enhanced CO2 photoreduction through surface/interface synergy.

Photocatalytic CO2 reduction into valuable fuel and chemical production has been regarded as a prospective strategy for tackling with the issues of the increasing of greenhouse gases and shortage of sustainable energy. A composite photocatalysis system employing a semiconductor enriched with oxygen vacancy and coupled with metallic cocatalyst can facilitate charge separation and transfer electrons. In this work, mesoporous TiO2 and titanium-based perovskite oxides (BaTiO3 and SrTiO3) nanoparticle assembly incorporated with abundant oxygen vacancy and copper particles have been successfully synthesized for CO2 photoreduction. As an example, the TiO2 decorated with different amounts of Cu particles has an impact on photocatalytic CO2 reduction into CH4 and CO. Particularly, the optimal TiO2/Cu-0.1 exhibits nearly 13.5 times higher CH4 yield (22.27 µmol g-1 h-1) than that of pristine TiO2 (1.65 µmol g-1 h-1). The as-obtained BaTiO3/Cu-0.1 and SrTiO3/Cu-0.1 also show enhanced CH4 yields towards photocatalytic CO2 reduction compared with pristine ones. Based on the temperature programmed desorption (TPD) and photo/electrochemical measurements, the co-embedding of Cu particles and abundant oxygen vacancy into the titanium-based oxides could promote CO2 adsorption capacity as well as separation and transfer of photoinduced electron-hole pairs, and finally result in efficient CO2 photoreduction upon the TiO2/Cu, SrTiO3/Cu, and BaTiO3/Cu composites.

Synergistic mediation of metallic bismuth and oxygen vacancy in Bi/Bi2WO6-x to promote 1O2 production for the photodegradation of bisphenol A and its analogues in water matrix.

Bi/Bi2WO6-x heterostructures has been successfully prepared by a facile one-step hydrothermal method. By maneuvering reaction time and Bi/W molar ratio of the precursors, we have been able to selectively introduce oxygen vacancy and metallic Bi into Bi2WO6 nanostructures. The obtained Bi/Bi2WO6-x heterostructures with more oxygen vacancy and moderate metallic Bi exhibit significantly improved photocatalytic activity for the photodegradation of bisphenol A (BPA) and its analogues due to its great ability for the generation of singlet oxygen (1O2), which has proven to work as the main reactive oxygen species during photocatalysis. It is also found the 1O2 concentration is highly depended on and modulated by the content of oxygen vacancy and metallic bismuth. Besides, we also demonstrate that the obtained Bi/Bi2WO6-x products display efficient photocatalytic performance toward BPA derivatives degradation and enhanced stability to resist the interferences in the water matrix.

Porous biochar-supported MnFe2O4 magnetic nanocomposite as an excellent adsorbent for simultaneous and effective removal of organic/inorganic arsenic from water.

To solve the problem of organic and inorganic arsenic species contamination in drinking water and/or wastewater, porous biochar-supported MnFe2O4 magnetic nanocomposite (BC-MF) was successfully fabricated and used as an excellent adsorbent for simultaneous removal of p-ASA and As(V) from water environment. This obtained BC-MF displayed remarkable adsorption performance for both p-ASA and As(V) removal at acidic and neutral pH (3-7), and di-anionic and mono-anionic species of p-ASA and As(V) facilitated the adsorption process. Specifically, BC-MF exceeded some reported adsorbents, and the adsorption capacities of p-ASA and As(V) were approximately 105 and 90 mg/g at a 10 µg/L equilibrium concentration. Satisfactory adsorption behavior including adsorption isotherms, competitive ions, humic acid (HA), and regeneration/reusability property in single and binary systems demonstrated the BC-MF can improve the potential application for arsenic-containing wastewater remediation. Proposed adsorption mechanism indicated that electrostatic interaction and surface complexation were involved the p-ASA and As(V) immobilization, whereas hydrogen bonding and π-π interactions may also contribute to the p-ASA removal. Additionally, the prominent sequestration p-ASA and As(V) performance in different water matrix and fixed-bed column studies indicated that BC-MF was a promising nanocomposite for simultaneously removal of organic and inorganic arsenic species in practical wastewater treatment.

New insights on nanostructure of ordered mesoporous FeMn bimetal oxides (OMFMs) by a novel inverse micelle method and their superior arsenic sequestration performance: Effect of calcination temperature and role of Fe/Mn oxides.

A series of ordered mesoporous FeMn bimetal oxides (OMFMs) were fabricated by using a novel inverse micelle method, and the texture, nanostructure and interface chemistry properties of OMFMs were closely correlated to the calcination temperature. Due to the amorphous regular inner-connected nanostructure and bimetallic synergistic effect, the obtained OMFMs exhibited superior arsenic sequestration performance than pure mesoporous Fe oxides (PMF) and Mn oxides (PMM). The optimum ratio of Fe/Mn and calcination temperature for arsenic removal was 3/1 and 350 °C (OMFM-3), and the maximum As(III) and As(V) adsorption capacities of OMFM-3 were 174.59 and 134.58 mg/g, respectively. Solution pH value negligibly affected the uptake of arsenic (ranged from 3.0 to 7.0), while SiO32-/PO43- ions and humic acid (HA) displayed significant inhibitory effect on arsenic removal by OMFM-3. According to the mechanism of arsenic removal, which simultaneously analyzed the arsenic redox transformation in aqueous phase and on solid phase interface, it was concluded that manganese oxides in OMFM-3 mainly played the role as a remarkable As(III) oxidant in water, whereas iron oxides dominantly acted as an excellent arsenic species adsorbent. Finally, the prominent arsenic sequestration behavior and performance in surface water suggested that OMFM-3 could be a promising and hopeful candidate for arsenic-contaminated (especially As(III)) surface water and groundwater remediation and treatment.

Cuprous ion (Cu+) doping induced surface/interface engineering for enhancing the CO2 photoreduction capability of W18O49 nanowires.

Solar-driven reduction of CO2 and H2O into fuels is a promising approach for addressing global warming and energy crisis. Herein, Cu+ doped W18O49 nanowires were prepared by a facile solvothermal method and applied in photocatalytic reduction of CO2. The composition and structure of pristine and Cu+ doped W18O49 samples have been characterized. It was found that the morphology of W18O49 nanowires was changed with increasing amounts of dopant. The photocatalytic CO2 reduction activity of W18O49 nanowires and the Cu+ doped W18O49 samples were evaluated using H2O as reducing agent. The strategy of Cu+ doping not only could affect the band edge position and the surface wettability, but also influenced separation of the photogenerated electron-hole pairs. It was found that Cu+ doping could introduce oxygen vacancy and change the conduction edge to a more negative position for W18O49 nanowires, which might be beneficial for the activation of CO2 and promote the following CO2 reduction. Furthermore, the higher separation efficiency of photogenerated electron-hole pairs with Cu+ doping could contribute to the CO2 photoreduction enhancement. In addition, the Cu+ doped W18O49 nanowires (Cu-W18O49-0.005) presented a relatively poor hydrophilic property, which might be beneficial for the adsorption of CO2 molecules and contribute to its superior photocatalytic CO2 reduction capability.

Facile inverse micelle fabrication of magnetic ordered mesoporous iron cerium bimetal oxides with excellent performance for arsenic removal from water.

In this study, magnetic ordered mesoporous Fe/Ce bimetal oxides (OMICs) were successfully synthesized via the modified sol-gel-based inverse micelle method. The textural/structure properties, surface chemistry and adsorption behavior of OMICs could be easily adjusted by using the calcination temperature. The sintering of samples would decrease the surface area, while expand the pore and crystallite size, which resulted in the formation of highly ordered inner-connected structure. Compared with pure mesoporous iron oxides (MI) and mesoporous cerium oxides (MC), this ordered mesoporous iron-cerium bimetal oxides (OMIC-3, 450 °C) exhibited remarkable arsenic adsorption performance. The maximum adsorption capacities of As(III) and As(V) for OMIC-3 were 281.34 and 216.72 mg/g, respectively, and both As(III)/As(V) adsorption kinetics were well described by the pseudo-second order. The ionic strength and coexisting ions (except SiO32- and PO43-) did not affect arsenic removal, while humic acid (HA) significantly influenced on the arsenic removal even at a lower concentration. The adsorption mechanism study revealed that both the surface charge and surface M-OH groups of OMIC-3 were played the key roles in arsenic removal. The reusable property suggested that this magnetic OMIC-3 was a promising excellent adsorbent for decontamination of arsenic-polluted (especially As(III)-polluted) wastewater.

Simultaneous removal of As(V)/Cr(VI) and acid orange 7 (AO7) by nanosized ordered magnetic mesoporous Fe-Ce bimetal oxides: Behavior and mechanism.

In this study, nanosized ordered magnetic mesoporous Fe-Ce bimetal oxides (Nanosized-MMIC) with highly well-ordered inner-connected mesostructure were successfully synthesized through the KIT-6 template method. This Nanosized-MMIC displayed excellent adsorption capacities for As(V), Cr(VI) and AO7, and the corresponding calculated maximum adsorption capacities of material were 111.17, 125.28 and 156.52 mg/g, respectively. As(V) and Cr(VI) removal by Nanosized-MMIC were slightly dependent on the ionic strength but highly solution pH-dependent, the coexistent silicate and phosphate ions competed remarkably with both As(V) and Cr(VI) for the adsorption active site. Mechanisms indicated As(V) and Cr(VI) formed inner-sphere complexes on Nanosized-MMIC interface via the electrostatic interaction and surface complexation, while the total organic carbon (TOC) change demonstrated that AO7 could be removed completely and no organic intermediates formed through the adsorption process. In addition, Nanosized-MMIC also possessed superior adsorption performance in As(V)/Cr(VI)-AO7 binary systems, and the reusable and regeneration properties indicated that the obtained nanomaterials could maintain at a comparatively high level after several recycling. Finally, fixed-bed experiments suggested the Nanosized-MMIC was expected to have a promising excellent nano-adsorbent with high application potential for co-existed toxic heavy metals and organic dyes removal in practical wastewater treatment.

Reutilization of iron sludge as heterogeneous Fenton catalyst for the degradation of rhodamine B: Role of sulfur and mesoporous structure.

Fenton process has gained considerable interest for its application in water treatment. However, the removal of iron sludge which generated during the process makes this method complex and uneconomical. In this study, we report a novel way of modifying iron sludge and use it as heterogeneous Fenton catalyst for the degradation of dye wastewater. It was found that after calcination at 600 °C, the iron sludge (Fe-600) exhibited much enhanced catalytic performance (99%) toward rhodamine B (RhB) in comparison with iron sludge without calcination (10%) in the presence of H2O2. The mesoporous structure of Fe-600 could facilitate its adsorption and immobilization of RhB, and the self-doped lattice sulfide played an important role during the Fenton degradation process. Moreover, the Fe-600 exhibited excellent heterogeneous Fenton degradation efficiency of acid red G and methylene blue as well. Our results may shed new light on the scalable preparation of novel heterogeneous Fenton catalysts and make contribution to the application of homogeneous Fenton degradation of wastewater.

Facile template-free fabrication of iron manganese bimetal oxides nanospheres with excellent capability for heavy metals removal.

Iron manganese bimetal oxides (IMBO) nanospheres were synthesized via a facile and environmentally friendly template-free approach. The obtained IMBO with large surface area and abundant surface functional groups exhibited excellent performance for heavy metals removal from aqueous solution, with the maximum adsorption capacities of As(V) and Cr(VI) were 132.77mg/g and 105.96mg/g, respectively. The adsorption mechanism study confirmed that except for electrostatic attraction, both surface hydroxyl group (OH-) and carbonate group (CO32-) simultaneously played a key role in the ion-exchange process with As(V) and Cr(VI) species, which finally formed inner-sphere surface complexes on the interface of IMBO. Furthermore, the remarkable removal of As(V) and Cr(VI) by fixed-bed column was also observed in the presence of various commonly competing anions, and the effective working capacities of IMBO for As(V) and Cr(VI) were approximately 410 pore volume (PV) and 320 pore volume (PV) when the breakthrough point was set at 10ppb. The exhausted IMBO could be easily regenerated by using a NaOH solution (0.1M). These results demonstrated that this IMBO was a potential and attractive adsorbent for the decontamination of arsenic/chromium polluted water system.

Nanocasted synthesis of magnetic mesoporous iron cerium bimetal oxides (MMIC) as an efficient heterogeneous Fenton-like catalyst for oxidation of arsenite.

Magnetic mesoporous iron cerium bimetal oxides (MMIC) with large surface area and pore volume was synthesized via the hard template approach. This obtained MMIC was easily separated from aqueous solution with an external magnetic field and was proposed as a heterogeneous Fenton-like catalyst for oxidation of As(III). The MMIC presented excellent catalytic activity for the oxidation of As(III), achieving almost complete oxidation of 1000ppb As(III) after 60min and complete removal of arsenic species after 180min with reaction conditions of 0.4g/L catalyst, pH of 3.0 and 0.4mM H2O2. Kinetics analysis showed that arsenic removal followed the pseudo-first order, and the pseudo-first-order rate constants increased from 0.0014min(-1) to 0.0548min(-1) as the H2O2 concentration increased from 0.04mM to 0.4mM. On the basis of the effects of XPS analysis and reactive oxidizing species, As(III) in aqueous solution was mainly oxidized by OH radicals, including the surface-bound OHads generated on the MMIC surface which were involved in Fe(2+) and Ce(3+), and free OHfree generation by soluble iron ions which were released from the MMIC into the bulk solution, and the generated As(V) was finally removed by MMIC through adsorption.

Nanocasted synthesis of ordered mesoporous cerium iron mixed oxide and its excellent performances for As(V) and Cr(VI) removal from aqueous solutions.

A novel ordered mesoporous cerium iron mixed oxide (OMCI) with high specific surface area and uniform and well-interconnected mesopores was synthesized through the nanocasting strategy using mesoporous silica (KIT-6) as a hard template. The obtained OMCI was used as an adsorbent to remove As(V) or Cr(VI) anions from aqueous solutions, and exhibited excellent performances with the maximum adsorption capacities of ~106.2 and ~75.36 mg g(-1) for As(V) and Cr(VI), respectively. A mechanism study showed that both Fe and Ce compositions participated in the As(V) or Cr(VI) adsorption process, and complex interactions were involved, including electrostatic attraction and the replacement of hydroxyl groups to form anionic negatively charged inner-sphere surface complexes. The OMCI material could be easily regenerated and reused while maintaining high adsorption capacities for As(V) and Cr(VI). Owing to their integrated features including high specific surface area, uniform and well-interconnected mesopores and specific acid-base surface properties, the synthesized OMCI material is expected to have good potential for the decontamination of As(V) or Cr(VI) polluted waters.