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Density functional theory (DFT) and Electrochemical Impedance Spectroscopy (EIS) were used to study the molecular adsorption behavior of the Co2+ doped TiO 2 (101) crystal plane, and the ethanol molecular gas sensitivity test was performed. Theoretical models indicate that doping leads to oxygen defects on the crystal plane and further chemisorption of two oxygen molecules, resulting in reduced electrical conductivity and improved oxygen storage capacity on the crystal plane. Ethanol molecules do not compete with N 2 , O 2 , and H 2 O molecules on doped crystal planes because of their different adsorption active sites, which means that the response time of gas-sensitive detection of ethanol molecules is short and is not interfered with the air molecules in the test environment. These results were confirmed by EIS and gas sensitivity experiments. The change of electrical conductivity after the adsorption of molecules on the crystal plane was confirmed by EIS. The enhanced oxygen storage capacity of the doped crystal plane was confirmed by the expansion of the linear response range of gas-sensitive detection from 20-100 ppm before doping to 20–1200 ppm. This provides a scientific basis for effectively shortening the gas-sensitive response time, increasing the concentration range, improving the oxygen-carrying capacity, and enhancing the catalytic and gas-sensitive properties of the material. [ABSTRACT FROM AUTHOR]

In this paper, the molecular adsorption behavior and photoelectric properties of tungsten trioxide monohydrate (WO 3 ·H 2 O) (002) crystal plane into tungsten trioxide (WO 3) (002) crystal plane were studied by Density Functional Theory (DFT) and Electrochemical Impedance Spectrum (EIS). DFT simulation shows that the adsorption active sites change from two to one after the transformation of WO 3 ·H 2 O (002) crystal plane to WO 3 (002) crystal plane, which further affects the molecular adsorption behavior of the crystal plane. The crystal plane conversion leads to the decrease of the adsorption energy of water (H 2 O) molecules and the increase of the adsorption energy of oxygen (O 2) molecules, which reduces the adverse effect of water molecules on the gas sensing performance of the material and enhances the adsorption of O 2 molecules. Like O 2 molecules and H 2 O molecules, the adsorption of four kinds of organic molecules on two crystal planes will lead to an increase in the conductivity of the crystal plane. The competitive adsorption of organic molecules with O 2 molecules leads to the decrease of the conductivity of both crystal planes. However, acetone (C 2 H 6 CO) molecules are combined in the form of hydrogen bond on the WO 3 ·H 2 O (002) crystal plane, and the contribution to the increase of the conductivity of the crystal plane is significantly higher than that of O 2 molecules. After the conversion to the WO 3 (002) crystal plane, this hydrogen bond disappears. These results were confirmed by EIS test experiments. The UV-Vis diffuse reflectance absorption spectra and photocurrent spectra show that the band gap increases after the WO 3 ·H 2 O (002) crystal plane is converted into the WO 3 (002) crystal plane. Understanding the influence of crystal plane transformation on molecular adsorption behavior and photoelectric properties is of great significance for optimizing the gas sensing properties and regulating the photoelectric properties of materials. • Crystal transformation affects the surface adsorption and photoelectric properties. • Density functional theory is used to simulate the crystal plane molecular adsorption. • The change of the active sites affects the molecular adsorption behavior. • Different molecules have competitive adsorption at the same adsorption active site. • The adsorption of molecules will change the crystal surface conductivity. [ABSTRACT FROM AUTHOR]

Six nonlinear, optical chromophores, Z1–Z6, based on the bis(N,N-diethyl)aniline-derived donor and thiolated isophorone bridge, were designed and synthesized. The bis(N,N-diethyl)aniline-derived donor was applied in a chromophore with thiolated isophorone as an electron bridge for the first time. In particular, the bridge parts of chromophores Z2–Z6 were modified with different functional groups, including tert-butyltrimethylsilane and tert-butyl(methyl)diphenylsilane derivative: 1,3-bis(trifluoromethyl)benzene and alkylaniline cyanoacetate, respectively. Density functional theory calculations suggested this series of chromophores show much greater hyperpolarizability than traditional, nonlinear, optical chromophores due to strong electron donor ability. These chromophores, Z1–Z6, showed very high poling efficiencies due to the large steric hindrance and hyperpolarizability of the chromophores. A large poling efficiency (2.04 ± 0.08 nm2/V2) and r33 value (193 pm/V) were achieved for polymeric thin films doped with 25 wt% chromophore Z6 at 1310 nm. [ABSTRACT FROM AUTHOR]

The gas-sensitive behavior of (221) and (110) crystal planes of SnO 2 to ethanol molecules were studied in this paper. The gas-sensitive detection results to 100 ppm ethanol showed that the response time of the (221) crystal plane is better than the (110) plane, which is 8 s and 62 s, respectively. The theoretical simulation shows that the gas-sensitive response time is determined by the adsorption speed of O 2 on the crystal plane. In the detection process of ethanol molecules, the O 2 molecules adsorbed on the crystal plane will be gradually consumed, causing the change of electrical conductivity on the crystal plane, to complete the gas sensitivity detection. In the air, N 2 , O 2 , and H 2 O molecules occupy the same active sites on the (110) crystal plane, and adsorption competition leads to the increased response time of gas-sensitive detection. However, the three molecules occupy different adsorption active sites on the (221) crystal plane, so the adsorption time of the O 2 molecule is shorter. Understanding the adsorption behavior of molecules on crystal planes is of great significance to the selection of gas-sensitive materials and the optimization of gas-sensitive properties. • The adsorption speed of O 2 determines the detection time of ethanol molecules. • The adsorption speed of O 2 depends on whether there is competitive adsorption. • Molecules occupy the same active site resulting in competitive adsorption. • O 2 and N 2 occupy the same active site on the SnO 2 110 plane, but not on the 221 plane. [ABSTRACT FROM AUTHOR]

In this paper, the molecular adsorption behavior of the SnO 2 (221) crystal plane is simulated by density functional theory, and the photoelectric properties of the crystal plane are studied. Through theoretical simulation, H 2 O, O 2 , and N 2 molecules are located on three different adsorption active sites of the crystal plane. The individual adsorption of the three molecules reduces the conductivity of the crystal plane. The conductivity increases when the molecules are co-adsorbed. The characteristic adsorption species (CAS) of the crystal plane are H 2 O and O 2 molecules. This is consistent with the experimental results of electrochemical impedance spectroscopy (EIS). The O 2 molecule shifts the response peak of the photocurrent spectrum to a low wavelength. Understanding the CAS of the crystal plane and its influence on the optical and electrical properties of materials has enlightening significance for further analysis of the photoelectric behavior of materials, and is helpful to provide the theoretical and experimental basis for the controllable design and synthesis of gas-sensitive materials. [Display omitted] • The characteristic adsorption species of the SnO 2 (221) crystal plane are H 2 O and O 2 molecules. • H 2 O, O 2 , and N 2 molecules have different adsorption active sites. • The individual adsorption of the three molecules alone decreases the crystal plane conductivity, but the co-adsorption increases it. • The response peak of the photocurrent spectrum for O 2 molecule adsorption shifts to a lower wavelength. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and electrochemical impedance spectroscopy (EIS) techniques are used to investigate the adsorption mode and evolution of O 2 molecules on the SnO 2 (221) crystal plane in this paper. The study shows that adsorbed O 2 molecules on the crystal plane exist in two reversible modes. In the general atmosphere, O 2 molecules are preferentially physically adsorbed on the crystal plane in the form of the mono-molecule, namely mode I; when the ambient oxygen concentration increases, it appears as a bi-molecular adsorption mode, namely mode II. Both modes decrease the crystal plane conductivity, but the decrease is more pronounced in mode II, which is also confirmed by EIS. In-depth exploration of the adsorption behavior of O 2 molecules is conducive to better understanding and control the surface state of materials and provides a basis for material design. • The surface adsorption of the material leads to the change of the crystal plane conductivity. • With the change of oxygen concentration, the two modes undergo mutual reversible conversion on the SnO 2 (221) crystal plane. • Two adsorption modes reduce the conductivity of the SnO 2 (221) crystal plane to different degrees. [ABSTRACT FROM AUTHOR]

In this study, hexagonal prism-shaped ZnO with exposed (002) and (200) planes is synthesized by using the hydrothermal method, and XRD and SEM images are used to confirm the results. Density functional theory (DFT) was used to simulate the characteristic adsorption species (CAS) of the hexagonal prism-shaped ZnO, and this revealed the mechanism of the CAS on the crystal surface. The results of simulations showed that O 2 and H 2 O molecules were chemically adsorbed on the (002) and (200) planes, respectively. As the rate of coverage of the (002) plane by oxygen molecules increased, its photocurrent and conductivity significantly increased, while the photocurrent spectrum moved to the direction of the long wave and appeared to have two peaks. The photocurrent and conductivity on the (200) plane did not change significantly with the increase in the rate of coverage by H 2 O molecules. The results of the theoretical simulations were consistent with the experimental results for the photocurrent spectrum. Therefore, the hexagonal prism-shaped ZnO can be used to detect reduced gas molecules by consuming adsorbed oxygen or using the photocurrent spectrum in gas-sensitive detection through a redox reaction. [Display omitted] • The CAS of hexagonal prism-shaped ZnO are O 2 and H 2 O molecules. • The O 2 molecule has an excellent oxygen-carrying capacity on the surface (002). • Gas sensing properties of hexagonal prism-shaped ZnO were investigated by DFT. [ABSTRACT FROM AUTHOR]

• ZnO nanoparticles were successfully synthesized by chemical precipitation method and doped on the surface of Co2+. • The effects of Co2+ doping on the characteristic adsorption species and optoelectronic properties of the ZnO crystal surface have been simulated by density functional theory (DFT). • The simulated data show the characteristic adsorption species of crystal plane changed before and after doping with Co2+. • The conductivity is proportional to the coverage rate before doping with Co2+, The conductivity is inversely proportional to the coverage rate after doping with Co2+. • The photocurrent spectrum fitting data is consistent with the regular of experimental data, indicating that the chemical adsorption of characteristic adsorbed O 2 and the conductivity of materials can be regulated by crystal plane Co2+ doping. The effects of Co2+ doping on the characteristic adsorption species and optoelectronic properties of the ZnO crystal plane have been simulated by Density Functional Theory (DFT). Because of the linear relationship between the Fermi level density of states and the conductivity, the conductivity is reacted by the Fermi level density of states. The simulated data show the characteristic adsorption species of crystal plane changed before and after doping with Co2+: The characteristic chemisorption species (CCS) O 2 molecules disappear after the ZnO (002) plane is doped with Co2+, CCS O 2 molecules appear after (200) plane is doped with Co2+, CCS H 2 O molecules appear after (110) plane is doped with Co2+. The conductivity decreases after doping with three crystal planes. The CCS of O 2 molecules has a significant effect on the conductivity. The CCS of H 2 O molecules has no obvious effect on the conductivity. The effect of O 2 molecular coverage rate of CCS on conductivity: The conductivity is proportional to the coverage rate of CCS before doping with Co2+, the conductivity is inversely proportional to the coverage rate of CCS after doping with Co2+. The photocurrent spectrum fitting data is consistent with the regular of experimental data, indicating that the chemical adsorption of characteristic adsorbed O 2 and the conductivity of materials can be regulated by crystal plane Co2+ doping, which plays a guiding role in regulating and making use of the characteristic O 2 absorption properties of the material plane. [ABSTRACT FROM AUTHOR]

• Considering experimental and theoretical aspects, the ORR performance of Pt/F-C was compared with that of Pt/C. • Improved strength and stability attained through the C-F bonds formed versus oxidation of the original C O and C C bonds. • An increased charge transfer from Pt to the F-C support is at the origin of the strong metal-support interaction. By combining experimental and theoretical aspects, this study focuses on exploring and enhancing the activity and stability towards oxygen reduction reaction (ORR) of fluorinated carbon supported platinum nanoparticles in the acidic electrolyte. Physical characterization results revealed that fluorinated carbon support generates a C-F bonding. The interaction between Pt and fluorinated-carbon allows for a strong charge transfer from Pt to the support. This phenomenon is consistent with the density functional theory (DFT) analysis. Because of the fluorination, the electronic structure of Pt is changed, which is an advantage for improving the catalytic activity and stability of the catalyst towards ORR. The ORR performance in Pt/F-C presented a significant improvement due to the adjustment of the electronic structure through the fluorinated carbon, and the formation of stronger C-F bonds versus the original C C bonds. [Display omitted] [ABSTRACT FROM AUTHOR]

When organic molecules are detected by gas-sensitive test, an oxidation-reduction reaction is triggered to consume adsorbed oxygen, and the change of material conductance resulting from the consumption of adsorbed oxygen is detected. In this paper, the molecular adsorption and gas-sensitive behavior of WO 3 (200) and (002) crystal planes are investigated. Density functional theory (DFT) simulations reveals that ethanol (C 2 H 5 OH) and oxygen molecules (O 2) have different adsorption active sites on the (200) and (002) crystal planes, there is no adsorption competition between C 2 H 5 OH molecules and O 2 molecules on the crystal plane, resulting the two crystal planes exhibit excellent selectivity for ethanol gas. Compared with other molecules, acetone (C 2 H 6 CO) and O 2 occupy the closest adsorption active sites on the (200) crystal plane, resulting in increased adsorption competition, which prolongs the response time and reduces the gas-sensitive selectivity. The molecular adsorption behavior holds important theoretical significance for studying the gas-sensitivity properties of materials. • The co-adsorption of ethanol and O 2 molecules makes selectivity of ethanol better. • Acetone molecules produce competitive adsorption with O 2 molecules. • WO 3 (200) and (002) crystal planes have different gas-sensitive selectivity. [ABSTRACT FROM AUTHOR]

Three novel chromophores B - D have been synthesized based on thiophene derivatived donors, including 5-(methyl(phenyl)amino)thiophene 5-(bis(4-methoxyphenyl)amino)thiophene 5-((4-methoxyphenyl)(methyl)amino)thiophene groups respectively, with the same isophorone-derived bridge and tricyanovinyldihydrofuran (TCF) acceptors. A new strategy was proposed to improve the electron donating ability of the chromophore, thienyl groups were explored as a replacement for the phenyl unit in the donor part of the chromophore. Density functional theory calculations suggested that the first hyperpolarizability of (arylamino) thiophene donor-containing chromophore B - D is about 20% higher than that of 4-(dialkylamino) phenyl counterpart chromophore A. At least 50% enhancement in bulk nonlinearity (r 33) is realized as the donor subunits were changed from alkylaniline to (arylamino) thiophene donors. Polymeric thin films doped with 25 wt% chromophore B - D have been poled to afford large r 33 values of 131, 143 and 138 p.m./V at 1.31 μm, respectively, which is much higher than the EO activity of chromophore A (88 pm/V). [Display omitted] • Three novel chromophores B-D with different thiophene-derived donor had been synthesized. • The r 33 value of film-C/PMMA and D/PMMA is 143 and 138 p.m./V, respectively, at 1.31 μm. • The decomposition temperatures of chromophores B-D are higher than 240 °C. [ABSTRACT FROM AUTHOR]

Developing room-temperature formaldehyde gas sensors with superior response-ability is crucial for many applications including the detection of indoor air pollutants. Herein, we synthesized a series of Ni-doped ZnO (Ni-ZnO) hierarchical porous structures decorated with NiS (NiS/Ni-ZnO) composite materials by the simple hydrothermal method, and the room-temperature (25 ± 1 ℃) UV light-activated photoelectronic formaldehyde sensors based on the ZnO, Ni-ZnO and NiS/Ni-ZnO composites were presented and compared. The response value of 0.2% NiS/0.4% Ni-ZnO material reached 330% toward 10 ppm formaldehyde gas, which was nearly 2.5 times higher than that of pure ZnO, and the faster response/recovery time (39.4 s/40.7 s) was obtained using UV light at room temperature. XPS, SPV, TPV spectrum analysis, and density functional theory (DFT) calculation showed that 0.2% NiS/0.4% Ni-ZnO sensor's excellent sensing performance was due to the synergistic effect of Ni doping and NiS modification which improved the separation efficiency and accelerated the migration of charge carriers. Here, the relationship between the response time of photoelectric gas sensors and the behavior of photogenerated carriers is firstly discussed in detail, which provides new insight into the development of room-temperature photoelectric gas sensors with superior response-ability. • NiS/Ni-ZnO hierarchical porous structure has been fabricated using hydrothermal method. • NiS/Ni-ZnO sensor exhibits fast response and high responsivity to formaldehyde at room temperature. • Excellent gas sensing performance of NiS/Ni-ZnO sensor is explained from the dynamic behavior of photogenerated carriers. • The relationship between the response time of gas sensor and the behavior of carriers is firstly discussed in detail. [ABSTRACT FROM AUTHOR]