NIR Diffuse Reflectance Spectra Research Articles

Oxygen vacancy-rich BiO2-x ultra-thin nanosheet for efficient full-spectrum responsive photocatalytic oxygen evolution from water splitting

Photocatalytic water splitting is an environmentally friendly technique for oxygen evolution. Vacancy-rich layered materials with good electromigration properties are of great interests. Herein, we synthesized full-spectrum responsive vacancy-rich BiO2-x ultra-thin nanosheets (UTNSs). The band gap is narrowed and the edge of valence band is increased in the BiO2-x UTNSs, which are responsible for the enhanced light response and are confirmed by UV–Vis–NIR diffuse reflectance spectra (DRS), electronic spin resonance (ESR), X-ray photoelectron spectroscopy (XPS) and valence measurement. Compared to Bi2O3 nanosheets (NSs), BiO2-x UTNSs exhibits enhanced photocatalytic performance for oxygen evolution under full-spectrum irradiation, which can be attributed to the oxygen vacancies. The presence of oxygen vacancies in BiO2-x UTNSs promote the oxidation ability. This finding provides defect level understanding for developing highly efficient full-spectrum light responsive photocatalysts.

Four new deep ultraviolet borates with isolated B12O24 groups: Synthesis, structure, and optical properties

Four new deep ultraviolet (DUV) borates Li7Na2KRb2B12O24, Li7.35Na2.36K1.50Cs0.78B12O24, Li6.97Na2.63K1.24Cs1.15B12O24, and Li7.27Na2.67Rb2.06B12O24 have been produced by high temperature solution method in open air. The structural analysis suggests that they all crystallize in the same trigonal space group R3¯ (No. 148), and possess the identical isolated B12O24 groups. Structural comparison among alkali-metal borates with BnO2n in their chemical formulas have been discussed. In addition, infrared spectra were used to verify their structural validity. Furthermore, the UV–Vis–NIR diffuse reflectance spectra reveal that they exhibit short cutoff edges below 180 nm (6.88 eV). The first-principles theoretical studies carried out to increase the understanding of electronic structure and linear optical property.

Noncentrosymmetric cubic RbBSi2O6 polymorph with deep ultraviolet cut-off edge

By the introduction of Rb+ with large ionic radius and rigid SiO4 unit into borate, a noncentrosymmetric crystal, RbBSi2O6 polymorph has been obtained. Its structure was determined by single crystal X-ray diffraction technique, and it can be described as a three dimensional (3D) framework constructed by the Si/BO4 tetrahedra via corner-sharing O atoms, the Rb atoms reside in the tunnels and large cavities of the 3D framework. In addition, the optical properties of RbBSi2O6 and CsBSi2O6, including IR spectra, UV–Vis–NIR diffuse reflectance spectra, have been reported in this work. Both RbBSi2O6 and CsBSi2O6 reveal short deep ultraviolet (UV) cutoff edges (below 180 nm and 185 nm, respectively), so they may have potential application in deep UV fields. Furthermore, the first-principle theoretical studies on band structure and density of states have also been performed for RbBSi2O6.

NaCa4V5O17 with isolated V2O7 dimer and V3O10 trimer exhibiting a large birefringence

A new NaCa4V5O17 compound has been synthesized by the solid-state method. It crystallizes in the triclinic space group P1̅ with unit cell parameters a = 6.9379(6) Å, b = 6.9523(6) Å, c = 15.5017(13) Å, α = 84.597(3)°, β = 87.276(3)°, γ = 86.860(3)°, and Z = 2. NaCa4V5O17 is the first compound in alkali and alkaline earth metal vanadate system with isolated V2O7 dimers and V3O10 trimers. The UV–Vis–NIR diffuse reflectance spectrum shows that NaCa4V5O17 exhibits wide transparent regions ranging from 345 nm to NIR. Thermal analysis and IR spectrum were also performed. In addition, band structure, density of states and birefringence of the title compound were calculated by the first-principles calculation for better understanding the structure-property relationships of NaCa4V5O17.

Two new mixed metal borates with the large birefringence in borates system confirmed by a disordered crystal optical calculation method

Two new mixed metal borates Pb6.33Sr1.67Cd(BO3)6 and Pb1.22Sr2.78Cd8(BO3)8 have been synthesized by the standard solid-state reaction method. Their structures were determined by single crystal X-ray diffraction. They crystallize in the different space groups, R3¯ for Pb6.33Sr1.67Cd(BO3)6 and C2/c for Pb1.22Sr2.78Cd8(BO3)8. The detailed structure comparison between Pb6.33Sr1.67Cd(BO3)6 and Pb1.22Sr2.78Cd8(BO3)8 shows that the main difference in their structures mainly originates from the effect of the cations on the structures. Other functional properties including UV–vis–NIR diffuse reflectance spectrum, IR spectrum, and thermal analysis are also performed on the reported compounds. In addition, in this work, a time-saving optical properties calculation method for disordered crystals was proposed and the results indicate that the title compounds have large birefringences in borates system.

Two noncentrosymmetric polyphosphates featuring infinite one-dimensional (PO3)∞ chain, LiMP2O6 (M = Rb, Cs): Synthesis, structure and optical properties

Two noncentrosymmetric polyphosphates, namely LiCsP2O6 and LiRbP2O6 have been synthesized from the high temperature solution. The structural analysis suggests that both of them crystallize in orthorhombic space group Fdd2 (No.43), with lattice parameters: a = 18.517(4) Å, b = 19.037(4) Å, c = 13.011(3) Å, and Z = 32 for LiRbP2O6, while a = 19.009(13) Å, b = 19.402(13) Å, c = 13.180(9) Å, and Z = 32 for LiCsP2O6. In the structure, the PO4 polyhedra are connected through corner-sharing to form 1D infinite (PO3) ∞ chains stretching along the c axis, which are further linked by the LiO4 polyhedra to construct a 3D framework with two types of tunnels. And the Rb/Cs atoms are filled in or around the periphery of the tunnels to keep the charge equilibrium. The IR spectra verify their structural validity. In addition, other characterizations including the UV−vis−NIR diffuse reflectance spectra, as well as first-principles theoretical studies have been performed on the two compounds.

Quaternary sulfide Ba5Cd2Ga2S10 containing chains of edge- and corner-sharing tetrahedra

The quaternary sulfide Ba5Cd2Ga2S10 was prepared by reaction of BaS, CdS, and Ga2S3 at high temperatures. Single-crystal X-ray diffraction analysis revealed that it adopts a new orthorhombic structure type (space group Pccn, Z = 4, a = 12.7664(7) Å, b = 12.8060(7) Å, c = 12.1265(7) Å) consisting of one-dimensional anionic chains [CdGaS5]5– built from edge- and corner-sharing tetrahedra centred by Cd and Ga atoms in an ordered fashion, with Ba2+ cations located between the chains. The UV–vis–NIR diffuse reflectance spectrum reveals two optical transitions at 1.92(2) and 3.29(2) eV, the latter being consistent with the yellow colour of the crystals.

Crystal structures and theoretical studies of polyphosphate LiZnP3O9 for nonlinear optical applications

Nonlinear optical materials have attracted worldwide attention owing to their wide range of applications, specially in the laser field. Phosphates with noncentrosymmetric structures are potential candidates for novel ultraviolet (UV)-NLO materials, because they usually display short UV cut-off edges. In this work, a polyphosphate, the LiZnP3O9 polyphosphate crystals were grown through spontaneous crystallization from high-temperature melts. It crystallizes in the orthorhombic space group P212121 with unit cell parameters a = 8.330(3) Å, b = 8.520(3) Å, c = 8.635(3) Å, and Z = 4. In the structure, all the P atoms are coordinated by four oxygen atoms forming the [PO4] tetrahedra and further connected to generate a zig-zag [PO3]∞ anionic framework. Thermal analysis, IR spectroscopy, UV–vis–NIR diffuse reflectance spectrum and powder second harmonic generation measurements are performed. In addition, the first-principles calculation was employed for better understanding the structure–property relationships of LiZnP3O9.

Synthesis, crystal structure and characterizations of a new diphosphate Rb2CaP2O7

A new diphosphate Rb2CaP2O7 is synthesized by solid-states reaction. This compound crystallizes in the monoclinic space group of P21/n, with unit cell parameters of a=10.0238(9) Å, b=5.7861(5) Å, c=13.0654(11) Å and β=104.726°. In this compound the [P2O7]4- dimers and [CaO6]10- units are interconnected by sharing the corner O atoms to form a 3D framework, with Rb+ cations filling in the interstices to balance the charge. The thermal property, IR and Raman spectra, UV–Vis–NIR diffuse reflectance spectrum and electronic band structure in Rb2CaP2O7 are determined, demonstrating its congruently melted characteristic and wide transparency down to the deep-ultraviolet region. Moreover, the replacement of Rb by K atoms in Rb2CaP2O7 can keep the compound structure unchanged, and the exemplified K1.85Rb0.15CaP2O7 exhibits almost the same fundamental physicochemical properties as Rb2CaP2O7.

Nondestructive measurement of internal quality attributes of apple fruit by using NIR spectroscopy

In this paper, a hybrid approach, which combines back propagation neural network (BPNN), generalized regression neural network (GRNN) and particle swarm optimization (PSO), is proposed to determine internal qualities in apples by using NIR diffuse reflectance spectra in the wavelength range of 400-1022 nm. The essence of the hybrid approach incorporates six phases. Firstly, the original spectral data should be submitted to Savitzky-Golay smoothing method to reduce noise. Secondly, using multiplicative scatter correction (MSC) on de-noised spectral data to modify additive and multiplicative effects. Thirdly, principal component analysis (PCA) is used to extract main features from the pretreated spectral data. Fourthly, obtaining forecasting results by using BPNN. Fifthly, obtaining forecasting results by using GRNN. Finally, these respective results are combined into the final forecasting results by using the principle of PSO. The hybrid model is examined by determining soluble solid content (SSC) and total acid content (TAC) of Green apples. Experimental results illustrate that the hybrid model shows great potential for internal quality control of apple fruits based on NIR spectroscopy.

M(1,2-dap)3][B10O13(OH)6] (M = Co, Ni): Two New Borates Containing [B10O13(OH)6]2− Cluster Units

Two novel isomorphic decaborates, [M(1,2-dap)3][B10O13(OH)6] (M = Co (1) and Ni (2); dap = 1,2-diaminopropane), with transition metal complexes [M(1,2-dap)3] as templates have been synthesized successfully under mild hydrothermal conditions and characterized by powder X-ray diffraction, thermogravimetric analysis, IR spectrum, single crystal X-ray diffraction and UV–Vis spectroscopy. The noodle-like orange/purple crystals crystallize in triclinic space group P-1. Their structure contain the isolated [B10O13(OH)6]2− clusters and further link together to produce a 3-D supramolecular framework with large channels by H-bonding interactions. The UV–Vis–NIR diffuse reflectance spectrum showed a wide-band-gap of 1 and 2. Notice that compounds 1 and 2 are not only the first isolated decaborate cluster and fill the gap left by the absence of isolated structures in the borate family but also could be considered as the structural building units to construct extended oxoboron cluster frameworks.

Vacancy‐Rich Monolayer BiO2−x as a Highly Efficient UV, Visible, and Near‐Infrared Responsive Photocatalyst

AbstractVacancy‐rich layered materials with good electron‐transfer property are of great interest. Herein, a full‐spectrum responsive vacancy‐rich monolayer BiO2−x has been synthesized. The increased density of states at the conduction band (CB) minimum in the monolayer BiO2−x is responsible for the enhanced photon response and photo‐absorption, which were confirmed by UV/Vis‐NIR diffuse reflectance spectra (DRS) and photocurrent measurements. Compared to bulk BiO2−x, monolayer BiO2−x has exhibited enhanced photocatalytic performance for rhodamine B and phenol removal under UV, visible, and near‐infrared light (NIR) irradiation, which can be attributed to the vacancy VBi‐O′′′ as confirmed by the positron annihilation spectra. The presence of VBi‐O′′′ defects in monolayer BiO2−x promoted the separation of electrons and holes. This finding provides an atomic level understanding for developing highly efficient UV, visible, and NIR light responsive photocatalysts.

Pb10V6O25: A new lead vanadate with apatite structure

The apatite-type crystal Pb10V6O25 has been grown from high temperature solution by spontaneous crystallization. It crystallizes in the hexagonal space group P63/m with lattice parameters a = 10.1045(6) Å, c = 7.3503(6) Å and Z = 1. The structure of Pb10V6O25 is composed of Pb(1)O9 polyhedra and VO4 tetrahedra, which form infinite Pb(1)V6O24 three-dimension (3D) framework with hexagonal star tunnels along the c axis, where Pb(2)3O(4) groups are filled. The band gap for Pb10V6O25 is calculated to be 2.86 eV, from the UV–Vis–NIR diffuse reflectance spectrum. First-principles calculations are performed to elucidate the electronic structure and optical properties. Thermal behavior and vibration spectroscopy of Pb10V6O25 are also reported in this work.

Noncentrosymmetric quaternary selenide Ba23Ga8Sb2Se38: Synthesis, structure, and optical properties

Reaction of BaSe, Ga2Se3, and Sb2Se3 yielded the quaternary selenide Ba23Ga8Sb2Se38 in the form of single crystals (at 1223 K) and phase-pure powder (at 1073 K). Ba23Ga8Sb2Se38 is isostructural to the sulfide analogue Ba23Ga8Sb2S38, crystallizing in the noncentrosymmetric orthorhombic space group Cmc21 with a = 9.9825(4) Å, b = 33.4658(13) Å, c = 13.3856(5) Å, and Z = 2. The structure consists of isolated GaSe4 tetrahedra and SbSe3 trigonal pyramids, separated by Ba cations. An optical band gap of 2.31(2) eV, consistent with the red-brown colour of the crystals, was deduced from the UV–vis–NIR diffuse reflectance spectrum. Nonlinear optical measurements using a fundamental laser wavelength of 2090 nm indicated that Ba23Ga8Sb2Se38 exhibits a moderate powder second harmonic generation signal and non-type-I phase-matching behaviour.

Color performance and near infrared reflectance property of novel yellow pigment based on Fe2TiO5 nanorods decorated mica composites

To obtain cool yellow pigments with high near-infrared reflectance, mica/Fe2TiO5 composite pigments were synthesized by a chemical liquid deposition method. The developed composite pigment powders were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis–NIR diffuse reflectance spectra, and CIEL*a*b* color scales. Different sized Fe2TiO5 nanorods were coated on the surface of mica particles. The particle size of the nanorods increased with increasing molar ratio of Fe3+ to Ti4+. The obtained composite pigments showed strong ultraviolet shielding ability and high near-infrared reflectance property. What's more, the Fe2TiO5 coating with smaller particle size possessed higher reflectance in the region of 700–1500 nm in accordance with the Kubelka-Munk theory. The near-infrared solar reflectance of mica/Fe2TiO5 composites was as high as 80.3%. An approximately 3 °C decrease in interior temperature was obtained for the heat box coated with the composite pigments. Furthermore, the composite pigments exhibit brilliant yellow colors. Therefore, mica/Fe2TiO5 composites are excellent near infrared reflective yellow pigments for efficient solar reflective coatings.

When one becomes two: Ba12In4Se20, not quite isostructural to Ba12In4S19

The ternary selenide Ba12In4Se20 was synthesized by reaction of BaSe, In2Se3, and Se at 1023 K. Single-crystal X-ray diffraction revealed a trigonal structure (space group R3¯, Z = 6, a = 10.0360(6) Å, c = 78.286(4) Å at room temperature) consisting of one-dimensional stacks of InSe4 tetrahedra, In2Se7 double tetrahedra, selenide Se2– anions, and diselenide Se22– anions, with Ba2+ cations in the intervening spaces. The selenide Ba12In4Se20 can be derived from the corresponding sulfide Ba12In4S19 by replacing one monoatomic Ch2– anion with a diatomic Ch22– anion. An optical band gap of 1.70(2) eV, consistent with the dark red colour of the crystals, was deduced from the UV–vis–NIR diffuse reflectance spectrum.

Noncentrosymmetric rare-earth selenides RE4InSbSe9 (RE = La–Nd)

Abstract The quaternary rare-earth selenides RE4InSbSe9 (RE = La–Nd) were prepared by reactions of RE, Sb2Se3, In2Se3, and Se at 1023–1123 K. They adopt the La4InSbS9-type structure (tetragonal, space group P41212, Z = 8, a = 10.4777(4)–10.6499(4) A, c = 29.0384(11)–29.4790(12) A) containing anionic helical chains [In2Sb2Se11]10− extending along the c-direction separated by La3+ cations and isolated Se2− anions. Consistent with the black colour of the crystals, an optical band gap of 1.76(2) eV was deduced from the UV–vis–NIR diffuse reflectance spectrum for the La member. Magnetic measurements on the Pr and Nd members indicated paramagnetic behaviour with no ordering down to 2 K.

Noncentrosymmetric chalcogenides BaZnSiSe4 and BaZnGeSe4 featuring one-dimensional structures

Abstract The two quaternary tetrel-containing selenides BaZnTtSe4 (Tt = Si, Ge) have been prepared by reactions of BaSe, ZnSe, Tt, and Se at 1023 K. They adopt noncentrosymmetric structures (orthorhombic, space group Ama2, Z = 4; a = 11.3055(8) A, b = 11.2344(7) A, c = 6.1994(4) A for BaZnSiSe4; a = 11.3255(6) A, b = 11.2527(6) A, c = 6.2917(3) A for BaZnGeSe4) that are of a new type consisting of one-dimensional chains of edge-sharing tetrahedra alternately centred by Zn and Tt atoms, with Ba cations separating the chains. The structure type is closely related to Sr2SnSe4 and NaEuAsS4. Large optical band gaps of 2.71(2) eV for BaZnSiSe4 and 2.46(2) eV for BaZnGeSe4, as deduced from UV–vis–NIR diffuse reflectance spectra, are consistent with the yellow or orange colour of the crystals. Nonlinear optical measurements on powder samples revealed that BaZnGeSe4 exhibited good second harmonic generation signals and type-I phase-matching behaviour using 2090 nm as the fundamental laser wavelength.

Facile synthesis of NiTiO3 yellow nano-pigments with enhanced solar radiation reflection efficiency by an innovative one-step method at low temperature

Inorganic NiTiO3 nano-pigments have received recent attentions as possible candidates for cool materials to be used in building roofs and facades. In this paper, we have attempted to develop an innovative low temperature pathway (processed at 50 °C) for obtaining NiTiO3 nanocrystals by an ultrasound-assisted wet chemical processing method. Different characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS) were used in order to characterize the size, morphology and optical responses of the obtained NiTiO3 nanoparticles. The crystallite size, particle size distribution range and band gap were found to be 10 nm, in the range of 10–20 nm and 3.72 eV, respectively. UV–Vis–NIR diffuse reflectance spectrum of NiTiO3 nanoparticles exhibited an intense reflection peak at around 580 nm, which is related to the brilliant yellow color of the synthesized nano-pigments. The enhanced reflectance seen in this work is much higher than that reported in similar works indicating these nano-pigments can be used as cool colorants for coating the building with better energy saving performance. Scanning electron microscopy studies indicated a uniform particle shape with a narrow size distribution. We believe that the methodology developed in this work provides a simple, cost-effective, and convenient route for synthesizing a variety of perovskite materials for assembling in nanotechnology.

Syntheses, characterization and theoretical studies of three apatite-type phosphates MPb4(PO4)3 (M = K, Rb, Cs)

Three phosphates MPb4(PO4)3 (M = K, Rb, Cs) have been synthesized by the high temperature melt method. The single-crystal X-ray structural analyses reveal that all of them belong to apatite-type phases and crystallize in the same space group, P63/m (no. 176). They exhibit a three dimensional (3D) structure that is composed of two kinds of channels constructed by [Pb(1)O6] and [PO4]. And the [Pb(2)|K(1)] ([Pb(2)|Rb(1)], [Pb(2)|Cs(1)]) atoms are located in the small channels. Detailed structural comparison indicates that the cations effect on the framework geometry is less obvious among the title compounds and the reported lead apatite-type phosphates, however, although MPb4(PO4)3 (M = K, Rb, Cs) have the similar stoichiometry with MM'4(BO3)3, the different coordination of the B and P atoms, as well as the cations effect make MPb4(PO4)3 and MM'4(BO3)3 crystallize in various space groups. The IR spectra were used to verify the validity of their structure. The TG-DSC analysis results indicate that KPb4(PO4)3 and RbPb4(PO4)3 melt congruently. The UV–Vis–NIR diffuse reflectance spectra indicate that they have no obvious absorption from 300 to 2500 nm. Optical properties as well as band structure calculations have been also performed based on density functional theory methods.