In this communication, pure D- or L-glutamic acid crystals can be obtained from a racemic solution by controllable addition of chiral seed crystals and ultrasonic-assisted recrystallization. In contrast, only racemic compounds were yielded under identical conditions in bulk solutions in the absence of an ultrasonic field.

We developed an effective and selective method to remove Cr(III) ions in acidic effluents. This method used combined ion imprinted technology with mesoporous silica materials. Cr(III) ion imprinted mesoporous silica (CrIMS) was synthesized and used as an excellent adsorbent. Iminodiacetic acid (IDA) was silanized, and acted as a functional monomer. The chemical groups, thermal stability, porosity and highly ordered morphology of CrIMS were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) isotherms, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The Brunauer–Emmett–Teller (BET) surface area was 856.24 m2 g−1. The saturated adsorption capacity of CrIMS towards Cr(III) ions reached up to 63 mg g−1 at pH 4.5. At a concentration of 200 mg L−1, the adsorption of Cr(III) ions reached equilibrium within 5 min and 20 min at pH 4.5 and pH 3.0, respectively. The CrIMS showed highly specific adsorption capacity and the imprinting factor was up to 4.03 at pH 3.0. The adsorption capacity of Cr(III) ions was remarkably higher than other co-existing metal ions. After eight adsorption–regeneration cycles, the adsorption efficiency of CrIMS still reached above 94.1%. The CrIMS could effectively remove Cr(III) ions below the discharge standard of China in real sample treatment.

This work demonstrates a simple strategy for producing highly selective adsorption magnetic ion imprinted mesoporous silica (MIIMS) nanocomposites. They have been functionalized by a γ-(aminoethylamino)propyl chelating group for specific recognition and rapid removal of toxic heavy metal ions from wastewaters. The superparamagnetic Fe3O4 nanocrystal was encapsulated in an imprinted mesoporous organosilica shell via a co-condensation synthesis method. The results of transmission electron microscopy (TEM) and small angle X-ray diffraction (XRD) confirmed that the imprinted mesoporous organosilica shell preserved a highly ordered 2D mesostructure. The Brunauer–Emmett–Teller (BET) analysis found the surface area was 946 m2 g−1. The saturated adsorption capacity of MIIMS toward cadmium reached up to 25.2 mg g−1 (0.224 mmol g−1) at pH 5.0. The adsorption of cadmium reached an equilibrium within 4.5 min. The results of a selectivity study revealed that the adsorption capacity for Cd2+ is much high than other co-existing heavy metal ions. The adsorption efficiency of MIIMS was above 94.2% after six extraction-stripping cycles. The MIIMS can efficiently remove cadmium ions in water treatment applications.

The pursuit of desirable longitudinal surface plasmon resonance (LSPR) of gold nanorods (AuNRs) and a suitable silica coating structure are two important aspects concerning mesoporous silica-coated gold nanorods (AuNR@mSiO2). This paper reports a simple approach to not only tailor the LSPR of AuNRs but also simultaneously control the structure and thickness of the silica shell after the silica coating process. Under acidic conditions, the use of O2 for end-selective etching of internal AuNRs shows good control over the aspect ratio of the AuNRs, thus enabling controllable tuning of the LSPR of AuNR@mSiO2. Compared to other strong oxidants such as aqua regia, O2 provides a milder and more gentle etching atmosphere, which gives the etched AuNRs good uniformity and regularity. Results showed that the thermal treatment of AuNR@mSiO2 solution before the initiation of the etching reaction had important impacts on the silica shell structure. Thermal treatment in ethanol solution gave rise to an empty and open mesoporous shell, and the use of ethanol–water as the solvent caused thinning of the shell thickness, while the internal AuNRs were basically unaffected in both cases. Both the opening and reduced thickness of the mesoporous silica shell facilitate the etching of the AuNRs. In addition, the rigid-type of mesoporous silica framework exposed in ethanol solution led to generation of cavity-possessing, rattle-type and hollow AuNR@mSiO2 as etching proceeded; however, in ethanol–water solution, the silica shell gained a certain extent of fluidity, resulting in movement of silica to fill the cavities created by end-etching of the internal AuNR.

Vibrational overtone studies primarily focus on X—H stretching overtone transitions, where X is an atom like C, O, N, or S. In contrast, the studies on the C═O stretching overtones are very scattered. To advance the research in this field, we measured the fundamental, first, and second overtones of the C═O stretching vibration of acetone and 2-hexanone in n-hexane, CCl4, and CHCl3, as well as in the vapor phase using FT-IR/FT-NIR spectroscopy. Density functional theory (DFT) calculations have also been performed to help the assignment of the C═O stretching bands and to guide interpretation of the experimental results. It was found that the wavenumbers, absorption intensities, and oscillator strengths of the C═O stretching bands show marked solvent dependence. In the fundamental and the first overtone regions, the intensities of the C═O stretching vibration were found to be pronouncedly more intense than those of the C—H stretching vibration. In the second overtone region, the intensities of the C—H stretching vibration are comparable to those of the C═O stretching vibration. The theoretical and observed decrease in integrated intensity upon going from the fundamental to the first overtone of the C═O stretching vibration is around 50, which is significantly larger than those of the O—H, C—H, and S—H stretching vibration. Both the calculated and experimental results suggest that excessive weakness in the C═O stretching overtone was shown to be a result of both a low anharmonicity and a substantial reduction in the oscillator strength. These results provide new insight into our understanding of the C═O stretching vibration.

•A new concept of infrared hybrid single-beam spectrum is introduced in this paper.•The unique advantage of the hybrid spectrum is that its intensity is closely related to a component factor.•Thus, a hybrid single-beam background spectrum with any desired intensity can be easily obtained simply by choosing an appropriate component factor.•This concept is applied to eliminating solvent bands and other background interferences successfully.For infrared (IR) spectral measurements, if a quality single-beam background spectrum with desired intensity could be obtained, the contributions from solvent and other background components could be completely suppressed and their bands would not appear in a final transmittance/absorbance spectrum. In order to achieve this ideal but difficult goal, the concept of hybrid single-beam spectrum is introduced in this paper. The hybrid single-beam spectrum (ϕh) is defined as a mixture of two single-beam spectra (ϕb1 and ϕb2) of the same sample but with different pathlengths (b1 and b2), namely, ϕh=αϕb1+(1−α)ϕb2, where α (0≤α≤1) is the component factor. The properties of the hybrid spectrum have been investigated. Under conditions of b2>b1≥0.7b2 and Amax≤0.60 (Amax is the maximum absorbance of b2 sample in the spectral range of interest), all the synthesized hybrid spectra are free from significant distortion regardless of the component factor. Therefore, the hybrid single-beam spectrum with desired intensity can be easily obtained simply by choosing an appropriate component factor. The proposed methodology has been demonstrated experimentally by the complete removal of the interference from the atmospheric water vapor and solvent.An infrared hybrid single-beam spectrum (ϕh) has been defined as a mixture of two single-beam spectra (ϕb1 and ϕb2) of the same sample but of different pathlengths (b1 and b2), namely, ϕh=αϕb1+(1−α)ϕb2 . The unique advantage of the hybrid spectrum is that its intensity is closely related to the component factor alpha (α). Thus, a hybrid background spectrum with any desired intensity can be easily obtained simply by choosing an appropriate component factor. Thus, it provides a convenient way of eliminating solvent/background interferences completely.

Catalytic degradation of organic dye molecules has attracted extensive attention due to their high toxicity to water resources. In this paper, we propose a novel method for the fabrication of uniform silver-coated ZnO nanowire arrays. The degradation of typical dye molecule rhodamine 6G (R6G), as an example, is investigated in the presence of the as-prepared silver-coated ZnO nanowire arrays. The experimental results show that such composite nanostructures exhibit high catalytic activity, and the reaction follows pseudo-first-order kinetics. Furthermore, these nanowire arrays are desirable SERS substrates for monitoring the catalytic degradation of dye molecules. Compared with traditional UV-visible spectroscopy, SERS technology can reflect more truly the catalytic degradation process occurring on the surface of the catalysts.

•The crystal polymorphs and morphologies highly depend on the solution depth.•This is the first study relating the type of polymorph with the depth of solution.•The concentration gradients are the main reasons to affect the polymorph formation.The polymorph control of calcium carbonate by the vapor diffusion method is still a challenging issue because the resultant crystal polymorphs and morphologies highly depend on the experimental setup. In this communication, we demonstrated that the concentration gradients accompanied by the vapor diffusion method (ammonia concentration, pH and the ratio of CO32− to Ca2+ are changed with the solution depth and with time) are probably the main reasons to significantly affect the formation of crystal polymorphs. Raman, SEM and XRD data showed that calcite and vaterite crystals were preferred to nucleate and grow in the upper or the lower areas of aqueous solution respectively. The above results can be explained by the gradient effect.

Catalytic degradation of organic dye molecules has attracted extensive attention due to their high toxicity to water resources. In this paper, we propose a novel method for the fabrication of uniform silver-coated ZnO nanowire arrays. The degradation of typical dye molecule rhodamine 6G (R6G), as an example, is investigated in the presence of the as-prepared silver-coated ZnO nanowire arrays. The experimental results show that such composite nanostructures exhibit high catalytic activity, and the reaction follows pseudo-first-order kinetics. Furthermore, these nanowire arrays are desirable SERS substrates for monitoring the catalytic degradation of dye molecules. Compared with traditional UV-visible spectroscopy, SERS technology can reflect more truly the catalytic degradation process occurring on the surface of the catalysts.

The pursuit of desirable longitudinal surface plasmon resonance (LSPR) of gold nanorods (AuNRs) and a suitable silica coating structure are two important aspects concerning mesoporous silica-coated gold nanorods (AuNR@mSiO2). This paper reports a simple approach to not only tailor the LSPR of AuNRs but also simultaneously control the structure and thickness of the silica shell after the silica coating process. Under acidic conditions, the use of O2 for end-selective etching of internal AuNRs shows good control over the aspect ratio of the AuNRs, thus enabling controllable tuning of the LSPR of AuNR@mSiO2. Compared to other strong oxidants such as aqua regia, O2 provides a milder and more gentle etching atmosphere, which gives the etched AuNRs good uniformity and regularity. Results showed that the thermal treatment of AuNR@mSiO2 solution before the initiation of the etching reaction had important impacts on the silica shell structure. Thermal treatment in ethanol solution gave rise to an empty and open mesoporous shell, and the use of ethanol–water as the solvent caused thinning of the shell thickness, while the internal AuNRs were basically unaffected in both cases. Both the opening and reduced thickness of the mesoporous silica shell facilitate the etching of the AuNRs. In addition, the rigid-type of mesoporous silica framework exposed in ethanol solution led to generation of cavity-possessing, rattle-type and hollow AuNR@mSiO2 as etching proceeded; however, in ethanol–water solution, the silica shell gained a certain extent of fluidity, resulting in movement of silica to fill the cavities created by end-etching of the internal AuNR.