Surface coordination induced a quasi p-n junction for efficient visible light driven degradation of tetracycline over hydroxyapatite.

The removal of antibiotics from aquatic solutions remains a global environmental challenge. In this work, the photocatalytic removal of a typical antibiotic-tetracycline (TC) using hydroxyapatite (HAp) as a catalyst was investigated. It was impressive that TC could be efficiently degraded by HAp under visible light irradiation, even though both HAp and TC exhibited poor harvesting in visible light region. The experimental and theoretical explorations were undertaken to thoroughly investigate the underlying mechanism of visible light degradation of TC over HAp. The results indicated that the formed TC-HAp complexes via surface coordination played an important role as photosensitizers for the visible light response. Together with the formation of a quasi p-n junction via band alignment, the photogenerated electrons in the highest unoccupied molecular orbital (HOMO) of TC-HAp were excited to the lowest unoccupied molecular orbital (LUMO) and subsequently migrated to the conduction band of HAp to achieve the efficient charge separation. Superoxide radicals and holes were found to be the major active species for TC degradation. The toxicity evaluation showed that TC could be transferred to the lower toxic intermediates, and deep oxidation with prolonged reaction time was necessary to eliminate the toxicity of TC. This work demonstrates the surface coordination with subsequent quasi p-n junction mechanism of TC degradation over HAp under visible light, which will stimulate us to explore new efficient photocatalytic systems for the degradation of various contaminants.

Rational Design of CoOOH/α-Fe2O3/SnO2 for Boosted Photoelectrochemical Water Oxidation: The Roles of Underneath SnO2 and Surface CoOOH.

Hematite (α-Fe2O3) photoanode is a promising candidate for efficient PEC solar energy conversion. However, the serious charge recombination together with the sluggish water oxidation kinetics of α-Fe2O3 still restricts its practical application in renewable energy systems. In this work, a CoOOH/α-Fe2O3/SnO2 photoanode was fabricated, in which the ultrathin SnO2 underlayer is deposited on the fluorine-doped tin oxide (FTO) substrate, α-Fe2O3 nanorod array is the absorber layer, and CoOOH nanosheet is the surface modifier, respectively. The resulting CoOOH/α-Fe2O3/SnO2 exhibited excellent PEC water splitting with a high photocurrent density of 2.05 mA cm-2 at 1.23 V vs RHE in the alkaline electrolyte, which is ca. 3.25 times that of bare α-Fe2O3. PEC characterizations demonstrated that SnO2 not only could block hole transport from α-Fe2O3 to FTO substrate but also could efficiently enhance the light-harvesting property and reduce the surface states by controlling the growth process of α-Fe2O3, while the CoOOH overlayer as cocatalysts could rapidly extract the photogenerated holes and provide catalytic active sites for water oxidation. Benefiting from the synergistic effects of SnO2 and CoOOH, the efficiency of the charge recombination and the overpotential for water oxidation of α-Fe2O3 are obviously decreased, resulting in the boosted PEC efficiency for water oxidation. The rational design and simple fabrication strategy display great potentials to be used for other PEC systems with excellent efficiency.

Insights into the multirole CoAl layered double hydroxide on boosting photoelectrochemical activity of hematite: Application to hydrogen peroxide sensing.

As an important compound in many industrial and biological processes, hydrogen peroxide (H2O2) would cause harmfulness to human health at high concentration level. It thus is urgent to develop highly sensitive and selective sensors for practical H2O2 detection in the fields of water monitoring, food quality control, and so on. In this work, CoAl layered double hydroxide ultrathin nanosheets decorated hematite (CoAl-LDH/α-Fe2O3) photoelectrode was successfully fabricated by a facile hydrothermal process. CoAl-LDH/α-Fe2O3 displays the relatively wide linear range from 1 to 2000 µM with a high sensitivity of 132.0 µA mM-1 cm-2 and a low detection limit of 0.04 µM (S/N ≥ 3) for PEC detection of H2O2, which is superior to other similar α-Fe2O3-based sensors in literatures. The (photo)electrochemical characterizations, such as electrochemical impedance spectroscopy, Mott-Schottky plot, cyclic voltammetry, open circuit potential and intensity modulated photocurrent spectroscopy, were used to investigate the roles of CoAl-LDH on the improved PEC response of α-Fe2O3 toward H2O2. It revealed that, CoAl-LDH could not only passivate the surface states and enlarge the band bending of α-Fe2O3, but also could act as trapping centers for holes and followed by as active sites for H2O2 oxidation, thus facilitated the charge separation and transfer. The strategy for boosting PEC response would be help for the further development of semiconductor-based PEC sensors.

Sensitive photoelectrochemical sensing of glucose using hematite decorated with NiAl-layered double hydroxides.

Hematite (α-Fe2O3) is a promising photoelectrode material for photoelectrochemical (PEC) sensors. However, it still suffers from serious surface charge recombination and slow interfacial charge transfer kinetics. In this work, NiAl-layered double hydroxides decorated on α-Fe2O3 (NiAl-LDH/α-Fe2O3) was successfully fabricated via a facile hydrothermal method. The NiAl-LDH/α-Fe2O3 exhibits excellent PEC response toward glucose, with a good linear range from 0.01 to 2 mM, a high sensitivity of 274.7 µA·mM-1·cm-2 and a low detection limit of 0.005 mM. NiAl-LDH/α-Fe2O3 PEC sensor could be used for glucose determination in various food samples, such as bread, toast and glucose oral solution, which achieved comparable results with that of HPLC. PEC and electrochemical characterizations indicate NiAl-LDH could act as and/or provide active sites for glucose detection, enlarge the band bending and decrease the charge transfer resistance, thus significantly improve the PEC response of α-Fe2O3 toward glucose.

Hematite decorated with nanodot-like cobalt (oxy)hydroxides for boosted photoelectrochemical water oxidation.

Photoelectrochemical (PEC) water splitting has been considered as an alternative process to produce green hydrogen. However, the energy conversion efficiency of PEC systems was still limited by the inefficient photoanode. Cocatalysts decoration is regarded as an efficient strategy for improving PEC performance of photoanode. In this work, nanodot-like cobalt (oxy)hydroxides was rationally decorated on hematite to fabricate CoOOH/Fe2O3 photoanode. The resulted CoOOH/Fe2O3 exhibits a high photocurrent density of 1.92 mA cm-2 at 1.23 V vs. RHE, which is 2.6 times than that of bare Fe2O3. In addition, the onset potential displays a cathodic shift of ca. 110 mV, indicating that CoOOH can efficiently accelerate water oxidation kinetics over Fe2O3. The comprehensive PEC and electrochemical characterizations reveal that CoOOH could not only provide abundant accessible Co active sites for water oxidation, but also could passivate the surface states of Fe2O3, thus increase the carrier density and decrease the interfacial resistance. As a result, the PEC water oxidation performance over Fe2O3 was significantly boosted. This work supports that the roles of CoOOH cocatalyst is generic and such CoOOH could be used for other semiconductor-based photoanodes for outstanding PEC water splitting performance.

Feasibility of using ammonium iron (II) sulphate to passivate hexavalent chromium in polluted soil.

ABSTRACTThe use of ammonium iron (II) sulphate ((NH4)2Fe(SO4)2) to remediate soil contaminated with Cr (VI) was assessed. (NH4)2Fe(SO4)2 effectively remediated soil contaminated with Cr (VI) and, acted as a fertilizer by supplying nitrogen because it contains ammonium. The effects of the (NH4)2Fe(SO4)2 dose, water content, pH of the soil and the contact time were investigated. The amount of Cr (VI) leached from the most-polluted soil, determined using a leaching toxicity procedure using optimized conditions, was 347.64 mg kg-1 when the soil was untreated and 6.74 mg kg-1 when the soil was treated with (NH4)2Fe(SO4)2. Bio-utilizable Cr contributed 59.44% and 0.16% of the total Cr contents of the untreated and treated soil, respectively. The relatively stable Cr species contributed 24.92% and 98.38% of the total Cr contents of the untreated and treated soil, respectively. The results indicated that adding (NH4)2Fe(SO4)2 markedly decreased the risk of Cr being released from heavily contaminated soil by decreasing the availability of Cr in the soil. Overall, the results indicated that adding (NH4)2Fe(SO4)2 causes some Cr (VI) in contaminated soil to be reduced to Cr (III), and to form a precipitate, which decreases the risk of Cr being released. (NH4)2Fe(SO4)2 can be applied to soil contaminated with Cr (VI) on a large scale because it is cheap and simple to achieve.

Photoelectrochemical sensing and mechanism investigation of hydrogen peroxide using a pristine hematite nanoarrays.

In this paper, a facile hydrothermal combined with subsequent two-step post-calcination method was used to fabricate hematite (α-Fe2O3) nanoarrays on fluorine-doped SnO2 glass (FTO). The morphology, crystalline phase, optical property and surface chemical states of the fabricated α-Fe2O3 photoelectrode were characterized by scanning electron microscopy, X-ray diffraction, ultraviolet visible spectroscopy and X-ray photoelectron spectroscopy correspondingly. The α-Fe2O3 photoelectrode exhibits excellent photoelectrochemical (PEC) response toward hydrogen peroxide (H2O2) in aqueous solutions, with a low detection limit of 20 µM (S/N = 3) and wide linear range (0.01-0.09, 0.3-4, and 6-16 mM). Additionally, the α-Fe2O3 photoelectrode shows satisfying reproducibility, stability, selectivity and good feasibility for real samples. Mechanism analysis indicates, comparing with H2O, H2O2 possesses much more fast reaction kinetics over α-Fe2O3 surface, thus the recombination of photogenerated charges are reduced, followed by much more photogenerated electrons are migrated to the counter electrode via external circuit. The insight on the enhanced photocurrent, which is corelative to the concentration of H2O2 in aqueous solution, will stimulate us to further optimize the surface structure of α-Fe2O3 to gain highly efficient α-Fe2O3 based sensors.

Sensitive Detection of Rifampicin Based on Au-Carbon Nanocomposite.

Gold nanoparticles-supported Cabot Vulcan XC72R (Au/VXC72R) nanocomposite was synthesized by chemical reduction of gold (III) chloride with VXC72R. A novel electrochemical sensor based on the Au/VXC72R nanocomposite has been fabricated for the sensitive detection of rifampicin (RIF). Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the morphology, structure and compositions of the nanocomposite. Under the optimal conditions, the Au/VXC72R-chitosan/GCE can be used to determine RIF concentration in a linear range from 5 × 10-7 mol/L to 1 × 10-5 mol/L with the detection limit of 1.1 × 107 M (S/N = 3). The proposed approach exhibits good stability, acceptable reproducibility and applicability, which will probably bring widespread applications in quality monitoring in real samples.

Removal of hexavalent chromium by using red mud activated with cetyltrimethylammonium bromide.

The removal of hexavalent chromium [Cr(VI)] from aqueous solution by using red mud activated with cetyltrimethylammonium bromide (CTAB) was studied. The optimum operation parameters, such as CTAB concentration, pH values, contact time, and initial Cr(VI) concentration, were investigated. The best concentration of CTAB for modifying red mud was found to be 0.50% (mCTAB/VHCl,0.6 mol/L). The lower pH (<2) was found to be much more favourable for the removal of Cr(VI). Red mud activated with CTAB can greatly improve the removal ratio of Cr(VI) as high as four times than that of original red mud. Adsorption equilibrium was reached within 30 min under the initial Cr(VI) concentration of 100 mg L(-1). The isotherm data were analysed using Langmuir and Freundlich models. The adsorption of Cr(VI) on activated red mud fitted well to the Langmuir isotherm model, and the maximum adsorption capacity was estimated as 22.20 mg g(-1) (Cr/red mud). The adsorption process could be well described using the pseudo-second-order model. The result shows that activated red mud is a promising agent for low-cost water treatment.

Effect of crystallization of Cu2ZnSnSxSe4-x counter electrode on the performance for efficient dye-sensitized solar cells.

Cu2ZnSnSxSe4-x (CZTSSe) counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) are commonly developed with porous structures, but their high surface area could also retard electron transport processes owing to the abundant grain boundaries. Herein, we employed a convenient solution method and a rapid heating process to prepare well crystalline CZTSSe CEs in DSSCs. The influence of crystallization of CZTSSe film on DSSCs performances was discussed in depth. The thermogravimetric analysis, phase morphology, conductivity, and electrochemical characteristics of CZTSSe films were performed. It is found that the rapid heating process is beneficial to the formation of well crystalline film with large grains. As the porosity and grain boundaries in the bulk film are dramatically reduced with the enhanced crystallization, the charge transport process is gradually improved. Using cyclic voltammogram and electrochemical impedance spectroscopy measurements, we propose that the accelerating charge transport is of great importance to the photovoltaic performances of DSSCs due to their superior electrocatalytic activities. As the highest cell efficiency was achieved, well crystalline CZTSSe is an efficient CE catalytic material.

Phase-dependent photocatalytic H2 evolution of copper zinc tin sulfide under visible light.

CZTS exhibited apparently phase-dependent photocatalytic H2 evolution under visible light. Possible factors for the phase-dependent photocatalytic activity of CZTS were discussed in detail.

Determination of GPTMS and epoxy groups on GPTMS doped nanosilica composite by spectrofluorimetric analysis.

A spectrofluorimetric method was established for the quantitative determination of 3-glycidoxypropyltrimethoxysilane (GPTMS), based on the quantitative reaction between dihydroxyl of hydrated epoxy groups and potassium periodate generating formaldehyde and the reaction of the formaldehyde with acetylacetone in the presence of ammonium ions generating a new compound having yellow green fluorescence. The established method was then used to determine the purity of a commercially obtained GPTMS sample and the amount of epoxy groups on GPTMS doped nanosilica composite (GPTMS/nano-SiO2). The conditions such as the concentrations of ammonium salts and acetylacetone, pH value, coloring temperature, and coloring time were investigated in detail with respect to their effects on the fluorescence intensity. It was found that the established method is simple in terms of operation and can be used to practically determine the purity of GPTMS and the amount of epoxy groups on GPTMS/nano-SiO2 with good accuracy and reproducibility.