Study Of The Controlled Preparation Of Crystalline Fiber Red Phosphorus And Its Application In Sensitive Components

Two-dimensional materials,which are representative materials of the next era,will be vital to human production and life.The exploration of new twodimensional layered materials will greatly expand the physical properties and applications of two-dimensional materials,which has important scientific significance and application value.The crystalline fibrous red phosphorus(CFRP),an allotrope of black phosphorus(BP),which is a two-dimensional layered semiconductor with high anisotropy and catalytic activity,is one of the most promising candidates in the field of optoelectronics.However,up to date,the lack of effective solutions for the controlled scale-up growth of micro-nano structures of CFRP has greatly hindered further research and practical applications.Here,we achieved the top-down and bottom-up controllable preparation of CFRP micro-nano structures by low-pressure vapor-phase transport method.Further,we studied the sensing characteristics of sensitive elements based on CFRP materials from three-dimensional to low-dimensional processes to the ambient atmosphere(gas,humidity,and light).Our results revealed the potential of CFRP applications in sensitive elements and issues related to surface interface science.The main research work of this thesis is as follows.(1)The CFRP was prepared by low-pressure mineralization-assistedchemical vapor-phase transport(CVT)method.The structural transformation of amorphous red phosphorus(ARP)assisted by single elements Sn,Te,I,Pb and Bi and two-element mineralizer was investigated.The results showed that the element Sn can induce the structural transformation of ARP to red phosphorus type Ⅱ,and elements Te,I,Te&Pb and Te&Bi guided the production of CFRP.The ARP structure was converted to red phosphorus type Ⅴ by the mineralization of elements Pb,Bi,Te&Sn,I&Sn,Pb&Sn,Bi&Sn,Te&I and Pb&Bi,and the temperature modulation led to the development of ARP toward the polymeric[P12(4)]P2[structure with the assistance of Pb and Bi.The transition of the BP structure from the ARP structure was possible with the assistance of elements Sn&I,Pb&I and Bi&I,respectively.This work demonstrated the computational speculations made by Ilya et al.in elementassisted crystalline phosphorus synthesis,which enabled the preparation of crystalline phosphorus on a large scale.(2)The resistive gas sensor was prepared with CFRP as the sensitive element.The results showed that CFRP has high responsiveness and excellent repeatability to NHs in dry environment,excellent selectivity and fast response/recovery(11 s/1.4 s)to NH3 in various gases such as C3H6O,NO2,C8H10,C7H8,CH2O,C2H5O and NH3.According to the gas concentration sensitivity,it was estimated that the CFRP gas sensor can reach the NH3 detection limit of ppb,which is lower than the NH3 concentration allowed by ambient air quality standards(indoor:0.26 ppm;workshop:39.53 ppm)to prevent any health hazard.Furthermore,the potential mechanism for the excellent gas-sensitive performance of CFRP against NH3 was explored by density flooding theory calculations on CFRP.The differential charge density and bader analysis revealed the excellent physical adsorption capacity of NH3 on CFRP with respect to adsorption energy.Then,the in situ gas Raman and Fourier transform infrared spectroscopy characterization results also illustrated about it.(3)The humidity sensor was prepared with the instability of crystalline fiber red phosphorus(CFRP)under ambient atmosphere.The CFRP humidity sensor exhibited high response(Ig/Ia)of 2600 over the humidity range of 18.8%to 82%,with fast response/recovery time of 1.57 s/0.13 s and good repeatability.These excellent performances were derived from the unique properties of CFRP.Thus,the humidity sensor for people health detection was prepared with the excellent humidity sensing properties of CFRP.With the lower limit of humidity environment suitable for human health,45%,and the upper limit,38%,where microorganisms breed fastest,as the detection line,the response of the sensor was 17.78 and the response time/recovery time was 11.76 s/0.75 s.(4)We prepared successfully CFRP/oxide composites with CFRP as the carrier by using liquid phase exfoliation combined with ball milling to composite crystalline fiber red phosphorus and oxides(GO,ZrO2,TiO2),and applied them to the sensitive elements of humidity sensors.It was found that both CFRP@GO and CFRP@ZrO2 sensors showed significant enhancement in response relative to CFRP in the tested interval,and CFRP@TiO2 remained almost the same in terms of responsiveness.However,CFRP@TiO2 enhanced the response/recovery time of the sensor due to the accelerated adsorption/desorption rates on the material surface and between molecules by the composite of CFRP and TiO2.Correspondingly,the CFRP@GO sensor not only improved the response recovery/time,but also enhanced the responsiveness at the lower detection limit by about 1.5 times compared to CFRP.In combination with the long-term stability testing of the sensors,the lifetime of the CFRP@GO and CFRP@ZrO2 sensors was slightly improved,while CFRP@TiO2 exacerbated the decay of the sensor performance.In contrast,the CFRP@GO sensor not only improves the response but also accelerates the response/recovery time with good repeatability.(5)The heterojunction surfaces of crystalline fibrous red phosphorus and metal nanoparticles(Cu,Pt,Ag)were prepared by a self-adsorption method to combine high activity and stability of sensitive elements.Further,it tested the long-term stability and application potential of CFRP/Ag,CFRP/Pt and CFRP/Cu nanoparticle composites as humidity sensors for human health detection.It was found that the sensitivity of the CFRP@Cu and CFRP@Pt sensors remained almost the same as the CFRP sensor performance in the tested interval,however,the CFRP@Ag sensor showed a significant performance degradation phenomenon.In terms of sensor response rate,the response/recovery times of the CFRP@Ag and CFRP@Pt sensors were similar to the CFRP performance,and the response rate of the CFRP@Cu sensor was improved by about double.Furthermore,the long-term stability of the CFRP@Cu humidity sensor was 97.08%,which greatly improved the service life of the CFRP-based sensor.(6)This was achieved with the bottom-up preparation of centimeter-scale crystalline fiber red phosphorus micropillar arrays(CFRP-MP)by low-pressure vapor-phase transport method(LP-CVT)in order to control the directional transition from ARP to CFRP structures.In this study,the crystalline phases,energy bands and novel physical properties of the large-area CFRP-MP arrays were investigated.The crystallization kinetics of the directional transition from ARP to CFRP crystal structure was explored with the assistance of spherical differential electron microscopy characterization.Further self-powered photodetectors of CFRP/Ag Schottky junctions were prepared following the successful preparation of large-area CFRP-MP arrays,and discovered the photogenerated pyroelectric effect of CFRP-MPs.The maximum photoresponse and detection rate under 405 nm laser irradiation was 151.03 mA/W and 3.50×109 Jone,respectively.