3D Printed Electrochromic Supercapacitors with Ultrahigh Mechanical Strength and Energy Density.

With the accelerating update of advanced electronic gadgets, a great deal of attention is being paid today to the function integration and intelligent design of electronic devices. Herein, a novel kind of multitasking 3D oxygen-deficient WO3- x ∙ 2H2 O/Ag/ceramic microscaffolds, possessing simultaneous giant energy density, ultrahigh mechanical strength, and reversible electrochromic performance is proposed, and fabricated by a 3D printing technique. The ceramic microscaffolds ensure outstanding mechanical strength and stability, the topology optimized porous lattice structure provides developed surface area for coloration as well as abundant easily accessible channels for rapid ion transportation, and the bifunctional oxygen-defective pseudomaterials enable the large areal capacity and impressive electrochromic performance. As a result, this 3D-printed multitasking microscaffolds simultaneously perform structure-designable, electrochromic, compression resistant, and energy storage functions, behaving with true 3D structure with tailorable curvatures, excellent compressive strength (61.9 MPa), large color variations (>145% in b* value), good aesthetic visual quality as well as exciting electrochemical performances for energy storage including ultrahigh areal capacitance (10.05 F cm-2 at 5 mA cm-2 ), record-high energy density (0.60 mWh cm-2 ), and superior long-term cycling stability (88.6% capacity retention after 10 000 cycles). This work opens up the possibility for high-performance multi-functional coupling structural materials and integrated systems.

Tunable dielectric properties of mesoporous carbon hollow microspheres via textural properties.

In this study, mesoporous carbon hollow microspheres (PCHMs) with tunable textural properties have been prepared through a facile hard template etching method. The PCHMs were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, Raman spectra, and nitrogen adsorption and desorption systems. Uniform PCHMs with shell thickness ranging from 23 nm to 55 nm are realized. PCHMs with different textural properties can regulate dielectric and electromagnetic (EM) wave absorption effectively. The composite of paraffin wax mixed with 10 wt% PCHMs (the shell thickness of PCHMs is 35 nm) exhibits a minimum coefficient value of -53.8 dB at 8.8 GHz, with a thickness of 3.4 mm. Besides, it is remarkable that the effective absorption bandwidth covers all the X band with as low as a 10 wt% filler ratio, compared with other spherical EM wave absorbers. The excellent EM wave absorption capability of PCHMs can be ascribed to the better impendence matching and strong EM wave attenuation constant based on tunable textural properties. Our results provide a facile strategy to tune dielectric properties of spherical carbon absorbers based on textural properties, and can be extended to other spherical absorbers.

Preparation of nitrogen and sulfur co-doped ordered mesoporous carbon for enhanced microwave absorption performance.

Ordered mesoporous carbon nanomaterials (OMCs) co-doped with homogeneous nitrogen and sulfur heteroatoms were prepared by nanocasting with the pyrrole oligomer catalyzed by sulfuric acid as a precursor and ordered mesoporous silica SBA-15 as a hard-template. By multi-technique approach utilization, it was demonstrated that the N and S co-doped OMCs possessed high ordered mesoporous structures, large surface areas and homogeneous distribution of heteroatoms. As a microwave absorber, the as-prepared materials exhibited a minimum reflection loss (RL) of -32.5 dB at the thickness of 2.5 mm and an absorption bandwidth of 3.2 GHz (RL < -10 dB) in X-band (8.2-12.4 GHz). The good microwave absorption performance was mainly originated from the high electrical conductivity induced by the high surface activity and special structures. And microwave energy can be effectively attenuated through multiple reflections and absorptions in complex conductive network. The design strategy in this work would contribute to the production of a lightweight absorber, presenting a strong absorbency and a wide bandwidth in microwave frequency.

Microstructure Design and Dimensional Engineering of Nanomaterials for Electromagnetic Wave Absorption and Thermal Insulation.

Multifunctional materials integrated with electromagnetic wave absorption (EWA), thermal insulation, and lightweight properties are urgently indispensable for the flourishing advancement of space technology, which can simultaneously prevent electromagnetic detection and resist aerodynamic heating. To achieve excellent synergistic EWA and thermal insulation performance, the elaborate regulate the microstructure and dimension of nanomaterials has emerged as a captivating research direction. However, comprehending the structure-property relationships between microstructure, electromagnetic response, and thermal insulation mechanisms remains a significant challenge. Herein, a comprehensive perspective focuses on the microstructure design encompassing various dimensions of nanomaterials, providing a comprehensive understanding of correlations among structure, EWA, and thermal insulation. First, the cutting-edge mechanisms of EWA and thermal insulation are elaborated, followed by the relationship between the dimensions of nanomaterials. Moreover, the synergistic design methods of EWA and thermal insulation are explored. Lastly, this review summarizes the corresponding shortcomings and issues of current EWA-integrated thermal insulation materials and proposes breakthrough directions for the creation of materials with superior performance.

A Pyrophosphate Bifunctional Cathode with Inductive Effect for High-Voltage and Self-Charging Zinc Ion Battery.

With the growing demand for new energy storage devices, rechargeable aqueous zinc ion batteries (ZIBs) have attracted widespread attention due to their low cost and high safety. Among the cathode materials for ZIBs, polyanionic-based cathode materials with high voltage, high stability, and low cost have great potential. In this paper, tetragonal Na2VOP2O7 was prepared using a simple sol-gel method. The discharge platform voltage amounted to 1.8 V and had good rate and cycle performance due to the inductive effect of pyrophosphate. Then, a protective layer of Zn-hydroxyapatite (ZnHAP) modification was applied to the cathode surface, which can inhibit the hydrolysis of vanadium ions. The capacity was enhanced by 19 % after modification and the capacity retention after 100 cycles was also higher. Interestingly, the Na2VOP2O7 cathode also possesses a self-charging effect, recovering to 48 % of its initial capacity with an open-circuit voltage (OCV) of 1.1 V within a certain period, and light exposure can reduce the self-charging time by 83 %. These beneficial results indicate that the pyrophosphate bifunctional cathode with inductive effect has a great potential to construct high-voltage and multifunctional zinc ion battery.

Ultraflexible Ultrathin 3D/1D Hierarchical Interpenetrating Ni-MOF/CNT Buckypaper Composites: Microstructures and Microwave Absorption Properties.

Metal-organic frameworks (MOFs) have attracted attention due to their designable structures. However, recently reported MOF microwave-absorbing materials (MAMs) are dominated by powders. It remains a challenge to design MOF/carbon nanotube (CNT) composite structures that combine the mechanical properties of self-supporting flexibility with excellent microwave absorption. This work involves the hydrothermal approach to grow Ni-MOF of different microstructures in situ on the CNT monofilament by adjusting the molar ratio of nickel ions to organic ligands. Subsequently, an ultraflexible self-supporting Ni-MOF/CNT buckypaper (BP) is obtained by directional gas pressure filtration technology. The BP porous skeleton and the Ni-MOF with a unique porous structure provide effective impedance matching. The CNTs contribute to the conduction loss, the cross-scale heterogeneous interface generated by Ni-MOF/CNT BP provides rich interfacial polarization loss, and the porous structure complicates the microwave propagation path. All factors work together to give Ni-MOF/CNT BP an excellent microwave absorption capacity. The minimum reflection losses of Ni-MOF/CNT BPs decorated with granular-, hollow porous prism-, and porous prism-shaped Ni-MOFs reach -50.8, -57.8, and -43.3 dB, respectively. The corresponding effective absorption bandwidths are 4.5, 6.3, and 4.8 GHz, respectively. Furthermore, BPs show remarkable flexibility as they can be wound hundreds of times around a glass rod with a diameter of 4 mm without structural damage. This work presents a new concept for creating ultraflexible self-supported MOF-based MAMs with hierarchical interpenetrating porous structures, with potential application advantages in the field of flexible electronics.

Introduction of Nanoscale Si3N4 to Improve the Dielectric Thermal Stability of a Si3N4/P(VDF-HFP) Composite Film.

In order to improve the dielectric thermal stability of polyvinylidene fluoride (PVDF)-based film, nano silicon nitride (Si3N4) was introduced, and hence the energy storage performance was improved. The introduction of nano Si3N4 fillers will induce a phase transition of P(VDF-HFP) from polar ß to nonpolar α, which leads to the improved energy storage property. As such, the discharging energy density of Si3N4/P(VDF-HFP) composite films increased with the amount of doped Si3N4. After incorporating 10wt% Si3N4 in Si3N4/P(VDF-HFP) films, the discharging density increased to 1.2 J/cm3 under a relatively low electric field of 100 MV/m. Compared with a pure P(VDF-HFP) film, both the discharging energy density and thermal dielectric relaxor temperature of Si3N4/P(VDF-HFP) increased. The working temperature increased from 80 °C to 120 °C, which is significant for ensuring its adaptability in high-temperature energy storage areas. Thus, this result indicates that Si3N4 is a key filler that can improve the thermal stability of PVDF-based energy storage polymer films and may provide a reference for high-temperature capacitor materials.

Amorphous/Nanocrystalline, Lightweight, Wave-Transparent Boron Nitride Nanobelt Aerogel for Thermal Insulation.

At present, the new generation of aircraft is developing in the direction of high speed, long endurance, high mobility, and repeatability. Some studies have shown that the surface temperature of the radome can reach even 1800 °C as the flight speed of the aircraft increases. However, the antenna inside the radome cannot serve at this temperature. Consequently, a thermal insulation system with electromagnetic wave-transparent ability and high-temperature resistance is urgently needed to protect the antenna from working normally. An aerogel material is known as "solid smoke," with the lowest density currently. Because of its high porosity (>90%) and the characteristics of nanopore size, its application in the field of thermal insulation always draws the attention of researchers. In this work, a novel amorphous/nanocrystalline boron nitride (BN) nanobelt aerogel was synthesized successfully. The BN aerogel shows lightweight (18 mg/cm3), good thermal stability (1400 °C under an inert atmosphere and 750 °C under an air atmosphere), wideband wave-transparent performance (dielectric constant of 1.03 and dielectric loss of 0.016 at 4-18 GHz), and thermal insulation property (43 mW/(m·K) at room temperature and 73 mW/(m·K) at 600 °C). The BN aerogel is a suitable candidate as an electromagnetic wave-transparent thermal insulator and fire-resistant material. What is more, the structural stability of the BN aerogel is good (Young's modulus remains basically constant during the fatigue tests), and the energy loss coefficient (∼0.56) is high; it also has the potential to be a mechanical energy dissipative material. The study on the amorphous/nanocrystalline BN nanobelt aerogel provides a new idea for structure design and performance optimization of a high-temperature electromagnetic functional insulation material.

Formation and Evolution of Micro/Nano Periodic Ripples on 2205 Stainless Steel Machined by Femtosecond Laser.

The preparation of micro/nano periodic surface structures using femtosecond laser machining technology has been the academic frontier and hotspot in recent years. The formation and evolution of micro/nano periodic ripples were investigated on 2205 stainless steel machined by femtosecond laser. Using single spot irradiation with fixed laser fluences and various pulse numbers, typical ripples, including nano HSFLs (‖), nano LSFLs (⟂), nano HSFLs (⟂) and micro grooves (‖), were generated one after another in one test. The morphologies of the ripples were analyzed, and the underlying mechanisms were discussed. It was found that the nano holes/pits presented at all stages could have played a key role in the formation and evolution of micro/nano periodic ripples. A new kind of microstructure, named the pea pod-like structure here, was discovered, and it was suggested that the formation and evolution of the micro/nano periodic ripples could be well explained by the pea pod-like structure model.

Robust Ti3C2Tx MXene foam modified with natural antioxidants for long-term effective electromagnetic interference shielding.

MXenes have been proven to be outstanding lossy phase of advanced electromagnetic interference (EMI) shielding materials. However, their poor tolerance to oxygen and water results in fast degradation of the pristine two-dimensional (2D) nanostructure and fading of the functional performance. Herein, in this research, natural antioxidants (e.g., melatonin, tea polyphenols, and phytic acid) were employed to protect the Ti3C2Tx MXene from its degradation in order to achieve a long-term stability of the EMI shielding performance. The results showed that the synthesized composites comprised of antioxidants and Ti3C2Tx exhibited a decelerating degradation rate resulting in an improved EMI shielding effective (SE) stability. The antioxidation mechanism of the applied antioxidants is discussed with respect to the nanostructure evolution of the Ti3C2Tx MXene. This work contributes to the basic foundations for the further development of advanced MXenes for stable applications in the EM field.

Construction of Hollow Carbon Nanofibers with Graphene Nanorods as Nano-Antennas for Lower-Frequency Microwave Absorption.

Electromagnetic (EM) wave absorbers at a lower-frequency region (2-8 GHz) require higher attenuation ability to achieve efficient absorption. However, the impedance match condition and attenuation ability are usually inversely related. Herein, one-dimensional hollow carbon nanofibers with graphene nanorods are prepared based on coaxial electrospinning technology. The morphology of graphene nanorods can be controlled by the annealing process. As the annealing time increased from 2 to 8 h, graphene nanospheres grew into graphene nanorods, which were catalyzed by Co catalysts derived from ZIF-67 nanoparticles. These nanorods can play the role of nano-antennas, which can guide EM waves into materials to enhance impedance match conditions. As a result, the carbon nanofibers with graphene nanorods possess a larger impedance match area with higher attenuation ability. The minimum reflection loss reaches -57.1 dB at a thickness of 4.6 mm, and the effective absorption bandwidth can cover almost both the S and C bands (2.4-8 GHz). This work contributes a meaningful perspective into the modulation of microwave absorption performance in the lower-frequency range.

Wide-temperature-range multispectral camouflage enabled by orientation-gradient co-optimized microwave blackbody metastructure coupled with conformal MXene coating.

Cloaking against electromagnetic detection is a well-researched topic; yet achieving multispectral camouflage over a wide temperature range remains challenging. Herein, an orientation-gradient co-optimized graded Gyroid-shellular (GGS) SiOC-based metastructure with a conformal MXene coating (M@SiOC) is proposed to achieve wide-temperature-range microwave/infrared/visible-light-compatible camouflage. Firstly, the combination of coordinate transformation and genetic algorithm endows the GGS architecture with optimal orientation and gradient, allowing superior microwave blackbody-like behavior. Secondly, a microwave-transparent, low-infrared-emissivity MXene metasurface is constructed in situ to permit wide-temperature-range infrared camouflage. Finally, the outstanding spectral selectivity of MXene enables camouflage against 1.06 µm-lidar and visible-light detection. As a result, the as-fabricated [110]-oriented GGS M@SiOC metamaterials exhibit outstanding wide-temperature-range multispectral camouflage: (i) ultrabroadband microwave absorption exceeding 80% in the X-Ku band from room temperature (RT) to 500 °C with absorption above 86.0% (91.4% on average) at 500 °C; (ii) excellent long-wavelength infrared camouflage for object temperatures from RT to 450 °C, reaching an infrared signal intensity of 78.5% for objects at 450 °C; and (iii) camouflage against both 1.06 µm-lidar and dark environment. Compared with traditional hierarchical metamaterials necessitating complex micro/nano-fabrication processes, this work provides a novel pathway toward the realization of structurally integrated multispectral stealth components by combining flexible metastructure design and high-fidelity additive manufacturing.

Decomposition reaction rate of BCl3-C3H6(propene)-H2 in the gas phase.

The decomposition reaction rate in the BCl(3)-C(3)H(6)-H(2) gas phase reaction system in preparing boron carbides was investigated based on the most favorable reaction pathways proposed by Jiang et al. [Theor. Chem. Accs. 2010, 127, 519] and Yang et al. [J. Theor. Comput. Chem. 2012, 11, 53]. The rate constants of all the elementary reactions were evaluated with the variational transition state theory. The vibrational frequencies for the stationary points as well as the selected points along the minimum energy paths (MEPs) were calculated with density functional theory at the B3PW91/6-311G(d,p) level and the energies were refined with the accurate model chemistry method G3(MP2). For the elementary reaction associated with a transition state, the MEP was obtained with the intrinsic reaction coordinates, while for the elementary reaction without transition state, the relaxed potential energy surface scan was employed to obtain the MEP. The rate constants were calculated for temperatures within 200-2000 K and fitted into three-parameter Arrhenius expressions. The reaction rates were investigated by using the COMSOL software to solve numerically the coupled differential rate equations. The results show that the reactions are, consistent with the experiments, appropriate at 1100-1500 K with the reaction time of 30 s for 1100 K, 1.5 s for 1200 K, 0.12 s for 1300 K, 0.011 s for 1400 K, or 0.001 s for 1500 K, for propene being almost completely consumed. The completely dissociated species, boron carbides C(3)B, C(2)B, and CB, have very low concentrations, and C(3)B is the main product at higher temperatures, while C(2)B is the main product at lower temperatures. For the reaction time 1 s, all these concentrations approach into a nearly constant. The maximum value (in mol/m(3)) is for the highest temperature 1500 K with the orders of -13, -17, and -23 for C(3)B, C(2)B, and CB, respectively. It was also found that the logarithm of the overall reaction rate and reciprocal temperature have an excellent linear relationship within 700-2000 K with a correlation coefficient of 0.99996. This corresponds to an apparent activation energy 337.0 kJ/mol, which is comparable with the energy barrier 362.6 kJ/mol of the rate control reaction at 0 K but is higher than either of the experiments 208.7 kJ/mol or the Gibbs free energy barrier 226.2 kJ/mol at 1200 K.

Micro/Nano Periodic Surface Structures and Performance of Stainless Steel Machined Using Femtosecond Lasers.

The machining of micro/nano periodic surface structures using a femtosecond laser has been an academic frontier and hotspot in recent years. With an ultrahigh laser fluence and an ultrashort pulse duration, femtosecond laser machining shows unique advantages in material processing. It can process almost any material and can greatly improve the processing accuracy with a minimum machining size and heat-affected zone. Meanwhile, it can fabricate a variety of micro/nano periodic surface structures and then change a material's surface performance dramatically, such as the material's wetting performance, corrosive properties, friction properties, and optical properties, demonstrating great application potential in defense, medical, high-end manufacturing, and many other fields. In recent years, the research is gradually deepening from the basic theory to optimization design, intelligent control, and application technology. Nowadays, while focusing on metal structure materials, especially on stainless steel, research institutions in the field of micro and nano manufacturing have conducted systematic and in-depth experimental research using different experimental environments and laser-processing parameters. They have prepared various surface structures with different morphologies and periods with sound performance, and are one step closer to many civilian engineering applications. This paper reviews the study of micro/nano periodic surface structures and the performance of stainless steel machined using a femtosecond laser, obtains the general evolution law of surface structure and performance with the femtosecond laser parameters, points out several key technical challenges for future study, and provides a useful reference for the engineering research and application of femtosecond laser micro/nano processing technology.

Rational design of n-Bi12TiO20@p-BiOI core-shell heterojunction for boosting photocatalytic NO removal.

Bismuth titanate (Bi12TiO20) with unique sillenite structure has been shown to be an excellent photocatalyst for environmental remediation. However, the narrow light-responsive range and rapid recombination of photoinduced electrons-holes limit the photocatalytic performance of Bi12TiO20. To overcome the limitations, a practical and feasibleway is to fabricate heterojunctions by combining Bi12TiO20 with suitable photocatalysts. Here, using a facile chemical precipitation method, a novel and hierarchical core-shell structure of n-Bi12TiO20@p-BiOI (BTO@BiOI) heterojunction was rationally designed and synthesized by loading BiOI nanosheets on BTO nanofibers. The constructed BTO@BiOI composites exhibited significant charge transfer ability due to the synergistic effects of the built-in electric field between BTO and BiOI as well as close interfacial contacts. In addition, the narrow bandgapcharacteristics of the BiOI led to wide light absorption ranges. Therefore, the BTO@BiOI heterojunction exhibited an improved photocatalytic performance under visible light irradiation. The NO removal efficiency of optimal BTO@BiOI was 45.7%, which was significantly higher compared tothat of pure BTO (3.6%) or BiOI (23.1%). Moreover, the cycling experiment revealed that BTO@BiOI composite has a good stability and reusability. The possible mechanism of photocatalytic NO oxidation over BTO@BiOI was investigated in detail.

Nature-Inspired 3D Spiral Grass Structured Graphene Quantum Dots/MXene Nanohybrids with Exceptional Photothermal-Driven Pseudo-Capacitance Improvement.

Solar-thermal conversion is considered as a green and simple means to improve the performance of energy storage materials, but often limited by the intrinsic photothermal properties of materials and crude structure design. Herein, inspired by the unique light trapping effect of wide leaf spiral grass during photosynthesis, a biomimetic structural photothermal energy storage system is developed, to further promote the solar thermal-driven pseudo capacitance improvement. In this system, three-dimensional printed tortional Kelvin cell arrays structure with interesting light trapping property functions as "spiral leaf blades" to improve the efficiency of light absorption, while graphene quantum dots/MXene nanohybrids with wide photothermal response range and strong electrochemical activity serve as "chloroplast" for photothermal conversion and energy storage. As expected, the biomimetic structure-enhanced photothermal supercapacitor achieves an ideal solar thermal-driven pseudo capacitance enhancement (up to 304%), an ultrahigh areal capacitance of 10.47 F cm-2 , remarkable photothermal response (surface temperature change of 50.1 °C), excellent energy density (1.18 mWh cm-2 ) and cycling stability (10000 cycles). This work not only offers a novel enhancement strategy for photothermal applications, but also inspires new structure designs for multifunctional energy storage and conversion devices.

Non-Destruction Evaluation Method for Long-Term Oxidation Behavior of SiC/SiC Composites with Different Preforms in Wet Oxygen.

The implementation of SiC fiber reinforced SiC/SiC composites to aero-engine hot components has attracted wide attention, due to their many excellent properties. Along these lines, in order to predict the oxidation behavior of the material in extreme environments and to explore the effect of different preforms on the oxidative behavior of the composites, four SiC/SiC composites, with different preforms, were oxidized under environmental conditions of pressure of 12 kPa H2O:8 kPa O2:80 kPa Ar, at 1400 °C temperature. Moreover, the morphology and defect distribution of the samples were characterized by carrying out scanning electron microscopy, and micro-computed X-ray tomography measurements. Furthermore, the relation between the micro- and macro-scales was established, so as to be able to predict the oxidation behavior of the composites; not only the quantitative relationship between the mass change rate and the defect volume change rate, but also the combination of micro-computed X-ray images.

Ti3 C2 Tx /MoS2 Self-Rolling Rod-Based Foam Boosts Interfacial Polarization for Electromagnetic Wave Absorption.

Heterogeneous interface design to boost interfacial polarization has become a feasible way to realize high electromagnetic wave absorbing (EMA) performance of dielectric materials. However, interfacial polarization in simple structures such as particles, rods, and flakes is weak and usually plays a secondary role. In order to enhance the interfacial polarization and simultaneously reduce the electronic conductivity to avoid reflection of electromagnetic wave, a more rational geometric structure for dielectric materials is desired. Herein, a Ti3 C2 Tx /MoS2 self-rolling rod-based foam is proposed to realize excellent interfacial polarization and achieve high EMA performance at ultralow density. Different surface tensions of Ti3 C2 Tx and ammonium tetrathiomolybdate are utilized to induce the self-rolling of Ti3 C2 Tx sheets. The rods with a high aspect ratio not only remarkably improve the polarization loss but also are beneficial to the construction of Ti3 C2 Tx /MoS2 foam, leading to enhanced EMA capability. As a result, the effective absorption bandwidth of Ti3 C2 Tx /MoS2 foam covers the whole X band (8.2-12.4 GHz) with a density of only 0.009 g cm-3 , at a thickness of 3.3 mm. The advantages of rod structures are verified through simulations in the CST microwave studio. This work inspires the rational geometric design of micro/nanostructures for new-generation EMA materials.

Tunable hydrogen enhancement of Ce3+ doped CdS with different Poisson's ratio support.

In this article, a 3D photocatalytic support with different Poisson's ratio was used for the first time to control the photocatalytic production rate of hydrogen. It was created by a stereo-lithography method, and the support with the most negative Poisson's ratio got the best result. The Poisson's ratio of the 3D structure influences the rate of hydrogen production, and it is important for the photocatalyst supports to be porous for light to penetrate into them. A series of Ce doped CdS photocatalysts were produced and immobilized on 3D multicellular Al2O3 supports. By changing the proportion of Ce3+ doped into the CdS photocatalysts 1 % of Ce3+ exhibited optimal hydrogen production, which was 222.9 % compared to that of the pure CdS. Using the 3D photocatalytic support with different Poisson's ratio, the photocatalytic production rate of hydrogen increased by 128 %.

Bi selectively doped SrTiO3-x nanosheets enhance photocatalytic CO2 reduction under visible light.

Converting CO2 into chemical energy by using solar energy is an environmental strategy to achieve carbon neutrality. In this paper, two dimensionality (2D) SrTiO3-x nanosheets with oxygen vacancies were synthesized successfully. Oxygen vacancies will generate defect levels in the band structure of SrTiO3-x. So, SrTiO3-x nanosheets have good photocatalytic CO2 reduction performance under visible light. In order to further improve its photocatalytic efficiency, Bi was used to dope Sr site and Ti site in SrTiO3-x nanosheets respectively. It is found that Sr site is the adsorption site of CO2 molecules. When Bi replaced Sr, CO2 adsorption on the surface of SrTiO3-x nanosheets was weakened. When Bi replaced Ti, there has no effect on CO2 adsorption. Due to the synergistic effect of Bi doping, oxygen vacancies, and Sr active site, the 1.0% Bi-doped Ti site in SrTiO3-x (1.0% Bi-Ti-STO) had the best photocatalytic performance under visible light (λ ≥ 420 nm). CO and CH4 yields were 5.58 umol/g/h and 0.36 umol/g/h. Photocatalytic CO2 reduction path has always been the focus of exploration. The in-situ FTIR spectrum proved the step of photocatalytic CO2 reduction and COO- and COOH are important intermediates in the photocatalytic CO2 reaction.