Effects of Annealing Temperature on Microstructure and Sensing Properties to Alcohol for Nano-La_(0.68)Pb_(0.32)FeO_3

La_(0.68)Pb_(0.32)FeO_3 samples annealed at different temperature were prepared using citrate sol-gel method. With increasing of annealing temperature from 200 to 1000 ℃, the samples crystallize to have single-phase perovskite structure. However, the sensitivity increases at first due to the improvement of crystallization of the perovskite phase, and finally drops attributed to the larger grain size. The optimal sensitivities for La_(0.68)Pb_(0.32)FeO_3 samples annealed at 400, 600, 800, and 1000 ℃ are 12.14, 14.77, 51.07, and 34.55, respectively.

Nanostructured materials with localized surface plasmon resonance for photocatalysis

Localized surface plasmon resonance (LSPR) enhanced photocatalysis has fascinated much interest and considerable efforts have been devoted toward the development of plasmonic photocatalysts. In the past decades, noble metal nanoparticles (Au and Ag) with LSPR feature have found wide applications in solar energy conversion. Numerous metal-based photocatalysts have been proposed including metal/semiconductor heterostructures and plasmonic bimetallic or multimetallic nanostructures. However, high cost and scarce reserve of noble metals largely limit their further practical use, which drives the focus gradually shift to low-cost and abundant nonmetallic nanostructures. Recently, various heavily doped semiconductors (such as WO_(3-x), MoO_(3-x), Cu_(2-x)S, TiN) have emerged as potential alternatives to costly noble metals for efficient photocatalysis due to their strong LSPR property in visible-near infrared region. This review starts with a brief introduction to LSPR property and LSPR-enhanced photocatalysis, the following highlights recent advances of plasmonic photocatalysts from noble metal to semiconductor-based plasmonic nanostructures. Their synthesis methods and promising applicability in plasmon-driven photocatalytic reactions such as water splitting, CO_(2) reduction and pollution decomposition are also summarized in details. This review is expected to give guidelines for exploring more efficient plasmonic systems and provide a perspective on development of plasmonic photocatalysis.

Nanocrystalline Gd_(1–x)Ca_xFeO_3 sensors for detection of methanol gas

The sol-gel method was used to prepare the nanocrystalline Gd_（1–x）Ca_xFeO_3 （x=0–0.4） powders. The XRD results showed that all the Gd_（1–x）Ca_xFeO_3 （x=0–0.4） compounds crystallized as perovskite phase with orthorhombic structure. The doping of Ca in GdFeO_3 not only reduced the resistance, but also enhanced the response to methanol. The Gd_（0.9）Ca_（0.1）FeO_3 showed the best response to methanol among Gd_（1–x）Ca_xFeO_3 sensors. Besides, it showed good selectivity to methanol among methanol, ethanol, CO and formaldehyde gases. The responses at 260 oC for Gd_（0.9）Ca_（0.1）FeO_3-based sensor to 600 ppm methanol, ethanol and CO gases were 117.7, 72.7 and 31.9, respectively. Even at quite low gas concentrations, Gd_（0.9）Ca_（0.1）FeO_3-based sensor had an obvious response. At 260 °C, the response of 1.54 was obtained to be 45 ppm methanol. The experimental results showed that nanocrystalline Gd_（0.9）Ca_（0.1）FeO_3 based sensor can be used to detect methanol gas.

Sensing performances to low concentration acetone for palladium doped LaFeO_3 sensors

The PdC12 was mixed with nanocrystalline powders LaFeO3 and subsequently followed by an annealing of 800 ℃. PdO phase was formed and almost distributed uniformly on the surface of LaFeO3 nano-particles. With an increase of PdO amounts in composite powders, sensing sensitivity Rg/Ra to low concentration acetone or ethanol for Pd doped LaFeO3 sensors increased at first, underwent the maximum with 2 wt.% PdC12 dopant, and then doped again. Interestingly, appropriate Pd doping in LaFeO3 changed the selectivity behavior of gas sensing. LaFeO3 sensor showed good selectivity to ethanol, but 2 wt.% Pd doped LaFeO3 sensor showed good selectivity to acetone. The sensitivity for LaFeO3 at 200 ℃was 1.32 to 1 ppm ethanol, and 1.19 to 1 ppm acetone. Whereas the sensitivity for 2 wt.% Pd doped LaFeO3 at 200 ℃ was 1.53 to 1 ppm ethanol, and 1.9 to 1 ppm acetone. The 2 wt.% Pd doped LaFeO3 sensor at 200 ℃ showed very short response time （4 s） and recovery time （2 s） to 1 ppm acetone gas, respectively. Such results showed that 2 wt.% Pd doped LaFeO3 sensor is a new promising sensing candidate for detecting low concentration acetone.

CO2 gas sensors based on Yb1-xCaxFeO3 nanocrystalline powders

In this study, the Yb（1-x）CaxFeO3（0≤x≤0.3） nanocrystalline powders were prepared by sol-gel method. We used the method of quantitative analysis to research the gas-sensitive properties for Yb（1-x）CaxFeO3 to CO2. Also, we investigated the effects of various factors on gas sensing properties by simple variable method. The doping of Ca could not only decrease the resistance of YbFeO3, but also enhance its sensitivity to CO2. When the Ca content x=0.2, Yb（1-x）CaxFeO3 showed the best response to CO2. The response Rg/Ra to 5000 ppm CO2 for Yb（0.8）Ca（0.2）FeO3 at its optimal temperature of 260 °C with the room temperature humidity of 28%RH was 1.85. The response and recovery time decreased with an increase of the operating temperature for Yb（0.8）Ca（0.2）FeO3 sensor to 5000 ppm CO2. Furthermore, with an increase of CO2 concentration from 1000 to 50000 ppm, the response time of Yb（0.8）Ca（0.2）FeO3 became shorter, and meanwhile the recovery time was longer. CO2-sensing response for Yb（0.8）Ca（0.2）FeO3 increased with the increase of relative humidity. The response for Yb（0.8）Ca（0.2）FeO3 in the background of air（with the room temperature humidity of 39%RH） at 260 °C could reach 2.012 to 5000 ppm CO2, which was larger than the corresponding value（1.16） in dry air.

Generation and modulation of multiple 2D bulk photovoltaic effects in space-time reversal asymmetric 2H-FeCl_(2)

The two-dimensional(2D)bulk photovoltaic effect(BPVE)is a cornerstone for future highly efficient 2D solar cells and optoelectronics.The ferromagnetic semiconductor 2H-FeCl_(2) is shown to realize a new type of BPVE in which spatial inversion(P),time reversal(T),and space−time reversal(PT)symmetries are broken(PT-broken).Using density functional theory and perturbation theory,we show that 2H-FeCl_(2) exhibits giant photocurrents,photo-spin-currents,and photo-orbital-currents under illumination by linearly polarized light.The injection-like and shift-like photocurrents coexist and propagate in different directions.The material also demonstrates substantial photoconductance,photo-spin-conductance,and photo-orbital-conductance,with magnitudes up to 4650(nm·μA/V^(2)),4620[nm·μA/V^(2)/(2e)],and 6450(nm·μA/V^(2)/e),respectively.Furthermore,the injection-currents,shift-spin-currents,and shift-orbital-currents can be readily switched via rotating the magnetizations of 2H-FeCl_(2).These results demonstrate the superior performance and intriguing control of a new type of BPVE in 2H-FeCl_(2).

CO_2 sensing properties and mechanism of PrFeO_3 and NdFeO_3 thick film sensor

The CO_2 sensing of PrFeO_3 and NdFeO_3 sensors were investigated. Experimental results show that the resistances for PrFeO_3 and NdFeO_3 in CO_2 gas are larger than those in air and the responses for PrFeO_3and NdFeO_3 sensors increase with an increase in room-temperature relative humidity. When exposed to1000 ppm CO_2, the response of PrFeO_3 thick film based on nano-powders annealed at 700℃can reach8.44 at 160℃for the background of wet air with 58%of room-temperature relative humidity (RH),which is much larger than the corresponding value (3.03) in wet air with 25%RH. The sensing response S of NdFeO_3 thick-film sensor based on nano-powders annealed at 600℃to 3000 ppm CO_2 at the operating temperature 200℃can reach 2.36 for the background of wet air with 72%RH, which is larger than the corresponding value (1.83) in the air with 25%RH. Compared with other CO_2 sensing materials, the PrFeO_3 sensor has larger response at lower operating temperature for CO_2 gas and may be used as a new CO_2 sensing material.

Studies on electrical properties and CO-sensing characteristics of La_(0.9) _(0.1)FeO_3

Semiconducting sensors offer an inexpensive and simple method for monitoring gases. Sensors based on the ABO3-type composite oxides materials have an advantage of high stability. The perovskite structures of these compounds are preserved, when an A-site deficiency of some perovskite structure compounds was formed. However, they exhibit particular physical properties. In this paper, La0.90.1FeO3 powder with an orthorhombic perovskite phase was prepared by sol-gel method. The electrical properties and CO-sensing characteristics of the La0.90.1FeO3 were also investigated. The results demonstrated that the La0.90.1FeO3 was a p-type semiconductor material. Compared with LaFeO3, the conductance of La0.90.1FeO3 was better than that of LaFeO3. The sensor based on La0.90.1FeO3 showed excellent CO gas-sensing characteristics.