Lexie Li - Academia.edu (original) (raw)

Papers by Lexie Li

Research paper thumbnail of Facile synthesis and ultrahigh ethanol response of hierarchically porous ZnO nanosheets

Sensors and Actuators B-chemical

Zinc oxide (ZnO) nanosheets were successfully synthesized through a facile, economic, and lowtemp... more Zinc oxide (ZnO) nanosheets were successfully synthesized through a facile, economic, and lowtemperature hydrothermal process, followed by annealing of the zinc carbonate hydroxide hydrate precursors. The nanosheets are single crystals with hexagonal wurtzite and mesoporous structures. Gas sensors based on these ZnO nanosheets exhibited ultrahigh response, fast response-recovery, and good selectivity and stability to 0.01-1000 ppm (parts per million) ethanol at 400 • C. Extremely low concentration ethanol (down to 10 ppb (parts per billion)) can be readily detected (S = 3.05 ± 0.21), which is the lowest detection limit to ethanol utilizing pure ZnO as sensing materials in a one-side heated gas sensor hitherto. The excellent ethanol-sensing performance of ZnO, particularly the ppb-level response, is mainly attributed to its novel hierarchical structure, which has a large specific surface area, abundant mesopores, single-crystal structure, plane-contact between sheets, three-dimensional network architecture, and characteristically small thickness.

Research paper thumbnail of A systematic study on evolution mechanism of titanate nanostructures in the hydrothermal process

Chemical Physics Letters, 2011

A systematic study on hydrothermal treatment of titania recording the changes of morphologies of ... more A systematic study on hydrothermal treatment of titania recording the changes of morphologies of titanate nanostructures was performed by subtly controlled termination of reaction and capture of intermediates. During the hydrothermal process, rapid coalescence of nanoparticles first occurred, followed by exfoliation of large aggregated moieties in their peripheries into nanosheets. The nanosheets were then rolled up to form short nanotubes. Afterwards, the nanotubes transformed into long ones, which eventually assembled into nanowires. This is a stepwise evolution process common for alkaline hydrothermal transitions. The oriented attachment (OA) model plays a vital role here, and the Oswald ripening (OR) mechanism appears to be effective as well.

Research paper thumbnail of High sensitive and selective formaldehyde sensors based on nanoparticle-assembled ZnO micro-octahedrons synthesized by homogeneous precipitation method

Sensors and Actuators B-chemical

Nanoparticle-assembled ZnO micro-octahedrons were synthesized by a facile homogeneous precipitati... more Nanoparticle-assembled ZnO micro-octahedrons were synthesized by a facile homogeneous precipitation method. The ZnO micro-octahedrons are hexagonal wurtzite with high crystallinity. Abundant structure defects were confirmed on ZnO surface by photoluminescence. Gas sensors based on the ZnO microoctahedrons exhibited high response, selectivity and stability to 1-1000 ppm formaldehyde at 400 • C. Especially, even 1 ppm formaldehyde could be detected with high response (S = 22.7). It is of interest to point out that formaldehyde could be easily distinguished from ethanol or acetaldehyde with a selectivity of about 3. The high formaldehyde response is mainly attributed to the synergistic effect of high contents of electron donor defects (Zn i and V O ) and highly active oxygen species (O 2− ) on the ZnO surface.

Research paper thumbnail of Shuttle-like ZnO nano/microrods: Facile synthesis, optical characterization and high formaldehyde sensing properties

Applied Surface Science, 2011

Shuttle-like ZnO nano/microrods were successfully synthesized via a low temperature (80 • C), "gr... more Shuttle-like ZnO nano/microrods were successfully synthesized via a low temperature (80 • C), "green" (without any organic solvent or surfactant) and simple hydrothermal process in the solution of zinc chloride and ammonia water. X-ray diffraction and Raman spectroscopy indicated that the ZnO nano/microrods are a well-crystallized hexagonal wurtzite structure. Yet photoluminescence analysis showed that abundant intrinsic defects (52.97% electron donor defects and 45.49% electron acceptor defects) exist on the surface of ZnO crystals. Gas sensors based on the shuttle-like ZnO nano/microrods exhibited high sensitivity, rapid response-recovery and good selectivity to formaldehyde in the range of 10-1000 ppm at an optimum operating temperature of 400 • C. Through applying linear fitting to the plot of sensitivity versus formaldehyde concentration in logarithmic forms, the chemisorbed oxygen species on the ZnO surface were found to be O 2− (highly active among O 2 , O 2 − and O − species). Notably, formaldehyde can be easily distinguished from acetaldehyde with a selectivity of about 3. The high formaldehyde sensitivity is mainly attributed to the synergistic effect of abundant electron donor defects (52.97%) and highly active oxidants (surface adsorbed O 2− species) co-existed on the surfaces of ZnO.

Research paper thumbnail of Hydrothermal synthesis of hierarchical nanoparticle-decorated ZnO microdisks and the structure-enhanced acetylene sensing properties at high temperatures

Sensors and Actuators B-chemical, 2011

Nanoparticle-decorated ZnO microdisks showing a hierarchical structure were successfully synthesi... more Nanoparticle-decorated ZnO microdisks showing a hierarchical structure were successfully synthesized through a citric acid-assisted hydrothermal process. The ZnO microdisks had a hexagonal wurtzite structure with high crystallinity. Sensors based on these microdisks exhibited high response values, fast response-recovery, good selectivity and long-term stability to 1-4000 ppm acetylene at 420 • C. In addition, even 1 ppm acetylene can be detected with high response (S = 7.9). The hierarchical structure can facilitate to fix the ZnO nanoparticles leading to a less aggregated configuration, which is expected to contribute much to the excellent acetylene sensing properties at high temperatures.

Research paper thumbnail of Facile synthesis and ultrahigh ethanol response of hierarchically porous ZnO nanosheets

Sensors and Actuators B-chemical

Zinc oxide (ZnO) nanosheets were successfully synthesized through a facile, economic, and lowtemp... more Zinc oxide (ZnO) nanosheets were successfully synthesized through a facile, economic, and lowtemperature hydrothermal process, followed by annealing of the zinc carbonate hydroxide hydrate precursors. The nanosheets are single crystals with hexagonal wurtzite and mesoporous structures. Gas sensors based on these ZnO nanosheets exhibited ultrahigh response, fast response-recovery, and good selectivity and stability to 0.01-1000 ppm (parts per million) ethanol at 400 • C. Extremely low concentration ethanol (down to 10 ppb (parts per billion)) can be readily detected (S = 3.05 ± 0.21), which is the lowest detection limit to ethanol utilizing pure ZnO as sensing materials in a one-side heated gas sensor hitherto. The excellent ethanol-sensing performance of ZnO, particularly the ppb-level response, is mainly attributed to its novel hierarchical structure, which has a large specific surface area, abundant mesopores, single-crystal structure, plane-contact between sheets, three-dimensional network architecture, and characteristically small thickness.

Research paper thumbnail of A systematic study on evolution mechanism of titanate nanostructures in the hydrothermal process

Chemical Physics Letters, 2011

A systematic study on hydrothermal treatment of titania recording the changes of morphologies of ... more A systematic study on hydrothermal treatment of titania recording the changes of morphologies of titanate nanostructures was performed by subtly controlled termination of reaction and capture of intermediates. During the hydrothermal process, rapid coalescence of nanoparticles first occurred, followed by exfoliation of large aggregated moieties in their peripheries into nanosheets. The nanosheets were then rolled up to form short nanotubes. Afterwards, the nanotubes transformed into long ones, which eventually assembled into nanowires. This is a stepwise evolution process common for alkaline hydrothermal transitions. The oriented attachment (OA) model plays a vital role here, and the Oswald ripening (OR) mechanism appears to be effective as well.

Research paper thumbnail of High sensitive and selective formaldehyde sensors based on nanoparticle-assembled ZnO micro-octahedrons synthesized by homogeneous precipitation method

Sensors and Actuators B-chemical

Nanoparticle-assembled ZnO micro-octahedrons were synthesized by a facile homogeneous precipitati... more Nanoparticle-assembled ZnO micro-octahedrons were synthesized by a facile homogeneous precipitation method. The ZnO micro-octahedrons are hexagonal wurtzite with high crystallinity. Abundant structure defects were confirmed on ZnO surface by photoluminescence. Gas sensors based on the ZnO microoctahedrons exhibited high response, selectivity and stability to 1-1000 ppm formaldehyde at 400 • C. Especially, even 1 ppm formaldehyde could be detected with high response (S = 22.7). It is of interest to point out that formaldehyde could be easily distinguished from ethanol or acetaldehyde with a selectivity of about 3. The high formaldehyde response is mainly attributed to the synergistic effect of high contents of electron donor defects (Zn i and V O ) and highly active oxygen species (O 2− ) on the ZnO surface.

Research paper thumbnail of Shuttle-like ZnO nano/microrods: Facile synthesis, optical characterization and high formaldehyde sensing properties

Applied Surface Science, 2011

Shuttle-like ZnO nano/microrods were successfully synthesized via a low temperature (80 • C), "gr... more Shuttle-like ZnO nano/microrods were successfully synthesized via a low temperature (80 • C), "green" (without any organic solvent or surfactant) and simple hydrothermal process in the solution of zinc chloride and ammonia water. X-ray diffraction and Raman spectroscopy indicated that the ZnO nano/microrods are a well-crystallized hexagonal wurtzite structure. Yet photoluminescence analysis showed that abundant intrinsic defects (52.97% electron donor defects and 45.49% electron acceptor defects) exist on the surface of ZnO crystals. Gas sensors based on the shuttle-like ZnO nano/microrods exhibited high sensitivity, rapid response-recovery and good selectivity to formaldehyde in the range of 10-1000 ppm at an optimum operating temperature of 400 • C. Through applying linear fitting to the plot of sensitivity versus formaldehyde concentration in logarithmic forms, the chemisorbed oxygen species on the ZnO surface were found to be O 2− (highly active among O 2 , O 2 − and O − species). Notably, formaldehyde can be easily distinguished from acetaldehyde with a selectivity of about 3. The high formaldehyde sensitivity is mainly attributed to the synergistic effect of abundant electron donor defects (52.97%) and highly active oxidants (surface adsorbed O 2− species) co-existed on the surfaces of ZnO.

Research paper thumbnail of Hydrothermal synthesis of hierarchical nanoparticle-decorated ZnO microdisks and the structure-enhanced acetylene sensing properties at high temperatures

Sensors and Actuators B-chemical, 2011

Nanoparticle-decorated ZnO microdisks showing a hierarchical structure were successfully synthesi... more Nanoparticle-decorated ZnO microdisks showing a hierarchical structure were successfully synthesized through a citric acid-assisted hydrothermal process. The ZnO microdisks had a hexagonal wurtzite structure with high crystallinity. Sensors based on these microdisks exhibited high response values, fast response-recovery, good selectivity and long-term stability to 1-4000 ppm acetylene at 420 • C. In addition, even 1 ppm acetylene can be detected with high response (S = 7.9). The hierarchical structure can facilitate to fix the ZnO nanoparticles leading to a less aggregated configuration, which is expected to contribute much to the excellent acetylene sensing properties at high temperatures.