Weixiong Liang - Academia.edu (original) (raw)

Papers by Weixiong Liang

Research paper thumbnail of Carbon Dots: Classically Defined versus Organic Hybrids on Shared Properties, Divergences, and Myths

Research paper thumbnail of Photoexcited State Properties of Poly(9-vinylcarbazole)-Functionalized Carbon Dots in Solution versus in Nanocomposite Films: Implications for Solid-State Optoelectronic Devices

Research paper thumbnail of Mechanistic Exploration of Visible Light-Activated Carbon/TiO2 Hybrid Dots Damaging Bacterial Cells

Applied Sciences

The carbon/TiO2 hybrid dots (C/TiO2-Dots) are structurally TiO2 nanoparticles (in the order of 25... more The carbon/TiO2 hybrid dots (C/TiO2-Dots) are structurally TiO2 nanoparticles (in the order of 25 nm in diameter from commercially available colloidal TiO2 samples) surface-attached by nanoscale carbon domains with organic moieties, thus equivalent to hybrids of individual TiO2 nanoparticles each decorated with many carbon dots. These hybrid dots with exposure to visible light exhibit potent antibacterial properties, similar to those found in neat carbon dots with the same light activation. The results from the use of established scavengers for reactive oxygen species (ROS) to “quench” the antibacterial activities, an indication for shared mechanistic origins, are also similar. The findings in experiments on probing biological consequences of the antibacterial action suggest that the visible light-activated C/TiO2-Dots cause significant damage to the bacterial cell membrane, resulting in higher permeability, with the associated oxidative stress leading to lipid peroxidation, inhibit...

Research paper thumbnail of Evaluation of Commercial “Carbon Quantum Dots” Sample on Origins of Red Absorption and Emission Features

C — Journal of Carbon Research, 2019

The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optic... more The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optical absorption and fluorescence emission methods; in reference to aqueous dispersed small carbon nanoparticles and representative carbon dots prepared from chemical functionalization of the carbon nanoparticles. The results suggest a very low content of carbon that is associated with nanoscale carbon particles/domains in the as-supplied sample; and likely significant contamination by dye-like species/mixtures. In the absence of any information on the synthesis and history of the commercial sample, the possible cause of the contamination was illustrated by an example on similar dye formation in the one-pot carbonization synthesis of “red carbon dots” from citric acid–formamide precursor mixtures under too mild processing conditions that were insufficient for the intended carbonization. The negative impacts to the carbon dots research field by the apparent proliferation and now commercial a...

Research paper thumbnail of On the myth of “red/near-IR carbon quantum dots” from thermal processing of specific colorless organic precursors

Nanoscale Advances

The thermal processing of specific precursor mixtures under relatively mild conditions does not r... more The thermal processing of specific precursor mixtures under relatively mild conditions does not result in “red/near-IR carbon dots” as previously claimed, but instead chemical reactions for molecular chromophores of red/near-IR absorptions.

Research paper thumbnail of Carbon Dots: Zero-Dimensional Carbon Allotrope with Unique Photoinduced Redox Characteristics

ACS Omega

Carbon dots (CDots) exploit and enhance the intrinsic properties of small carbon nanoparticles. T... more Carbon dots (CDots) exploit and enhance the intrinsic properties of small carbon nanoparticles. Their optical absorptions and photoinduced redox characteristics are competitive with those of conventional semiconductor quantum dots at one end and fullerenes and other carbon nanomaterials at the other. Highlighted in this mini review are the effective photon harvesting over a broad spectral range by CDots and their subsequent excited-state charge transfer processes and interactions, which have enabled their use as sensors, for photodynamic effects, and in various energy conversion technologies.

Research paper thumbnail of Carbon Dots as Potent Antimicrobial Agents

Research paper thumbnail of Carbon dots for energy conversion applications

Journal of Applied Physics

Quantum dots (QDs), generally referring to semiconductor nanocrystals that display the quantum co... more Quantum dots (QDs), generally referring to semiconductor nanocrystals that display the quantum confinement effect, have been widely pursued for many energy conversion applications. More recently, carbon dots (CDots), which are small carbon nanoparticles with various surface passivation schemes, have been found to possess optical properties and photoinduced redox characteristics resembling those of conventional semiconductor QDs and thus are amenable to some of the same uses in energy conversions. Among the various carbon nanomaterials, fullerenes have been extensively investigated for their use as critical components in optoelectronic devices and systems. Carbon nanoparticles, representing a largely ignored nanoscale carbon allotrope, are in fact more effective in some of the same functions, which are materialized and much enhanced upon the surface passivation of the nanoparticles in CDots. In this perspective article on CDots for energy conversion applications, the optical properties and redox characteristics of CDots, including the related mechanistic framework and its relationship to the use of CDots as potent photocatalysts for the conversion of CO 2 into small organic molecules, are highlighted. Also highlighted are results from representative studies using CDots in light-emitting diodes and various solar cells to demonstrate their excellent potential for a wide range of roles in optoelectronic devices and systems. Issues and opportunities in the further development of the CDots platform and related technologies are discussed.

Research paper thumbnail of Systematic Comparison of Carbon Dots from Different Preparations—Consistent Optical Properties and Photoinduced Redox Characteristics in Visible Spectrum and Structural and Mechanistic Implications

The Journal of Physical Chemistry C

Carbon dots (CDots) are characterized by their optical properties including strong absorptions an... more Carbon dots (CDots) are characterized by their optical properties including strong absorptions and bright and colorful fluorescence emissions in the visible spectrum and by their photoinduced redox characteristics as both potent electron acceptors and donors. The reported study was for a systematic comparison of CDots from different synthetic approaches based on the use of pre-existing small carbon nanoparticles sourced from pure carbon soot versus the formation of similar nanoparticles in situ via a one-pot thermal carbonization of organic molecular precursors, emphasizing spectroscopic characterizations over the visible spectrum. The results show that the CDots prepared by the latter under sufficiently robust processing conditions are generally no different from those from the former in terms of the observed optical properties and associated photoinduced redox characteristics in the application-wise more meaningful visible spectral region, suggesting a high stability or general applicability of the defi...

Research paper thumbnail of Hybrid carbon dots platform enabling opportunities for desired optical properties and redox characteristics by-design

Chemical Physics Letters

Abstract Carbon dots (CDots) exploit unique properties of small carbon nanoparticles, which repre... more Abstract Carbon dots (CDots) exploit unique properties of small carbon nanoparticles, which represent the often under-appreciated zero-dimensional carbon allotrope. The carbon nanoparticles in CDots could be modified by a selected organic chromophore of desired strong red/near-IR absorption in the dot synthesis to obtain a specific type of hybrid CDots. The reported results show that these hybrid CDots derived from the modification of core carbon nanoparticles by selected dyes or other chromophoric species represent a highly versatile and effective platform for CDots of desired optical properties and photoinduced redox characteristics in a by-design fashion.

Research paper thumbnail of Functionalization of Carbon Nanoparticles and Defunctionalization—Toward Structural and Mechanistic Elucidation of Carbon “Quantum” Dots

The Journal of Physical Chemistry C

Small carbon nanoparticles were functionalized by low-molecular weight amino compound 3-ethoxypro... more Small carbon nanoparticles were functionalized by low-molecular weight amino compound 3-ethoxypropylamine (EPA) for ultracompact carbon dots of bright fluorescence emissions. The results from solution-phase NMR characterization support the expected dot structure of carbon nanoparticles surface-attached with EPA species. The optical properties of the EPA-carbon dots share many features with those found in carbon dots of other surface functionalities, but there is an extra absorption shoulder in the blue spectral region, into which the excitation results in much enhanced green fluorescence emissions. The EPA-carbon dots were defunctionalized by gradually removing the EPA species from the carbon nanoparticles, along with spectroscopic characterizations on the samples of different degrees of defunctionalization. The outcomes further confirm the critical role of surface functionalization in the superior optical properties of carbon dots. Results from systematic measurements of fluorescence quantum yields and d...

Research paper thumbnail of A new approach in functionalization of carbon nanoparticles for optoelectronically relevant carbon dots and beyond

Carbon

Abstract Carbon dots (CDots), generally small carbon nanoparticles with surface passivation by a ... more Abstract Carbon dots (CDots), generally small carbon nanoparticles with surface passivation by a soft corona-like layer of mostly organic species, have been actively pursued for potential applications in optoelectronics, including various functions that have been served by some popular fullerene derivatives. For the preparation of CDots, chemical functionalization of pre-processed and selected small carbon nanoparticles by organic molecules, so far mostly molecules with primary and secondary amine groups, has been an effective method. In this study, carbon nanoparticles were functionalized by N-ethylcarbazole (NEC) under microwave-assisted reaction conditions for NEC-CDots, analogous but with advantages to the CDots of surface functionalization by poly(N-vinylcarbazole) (PVK, which holds a special place in optoelectronics). NEC molecules can apparently be activated under the reaction conditions for reactive functionalities such as radicals to bind to surface carbons of the nanoparticles, consistent with the observed high stability of NEC-CDots. These dots, likely with a unique surface passivation scheme, exhibited optical properties and photoinduced redox characteristics similar to those found in other high-performance CDots. The potentially broad applicability of the new functionalization approach is discussed, so are implications of the unique surface passivation of carbon nanoparticles by the carbazole moieties.

Research paper thumbnail of Carbon Dots: Classically Defined versus Organic Hybrids on Shared Properties, Divergences, and Myths

Research paper thumbnail of Photoexcited State Properties of Poly(9-vinylcarbazole)-Functionalized Carbon Dots in Solution versus in Nanocomposite Films: Implications for Solid-State Optoelectronic Devices

Research paper thumbnail of Mechanistic Exploration of Visible Light-Activated Carbon/TiO2 Hybrid Dots Damaging Bacterial Cells

Applied Sciences

The carbon/TiO2 hybrid dots (C/TiO2-Dots) are structurally TiO2 nanoparticles (in the order of 25... more The carbon/TiO2 hybrid dots (C/TiO2-Dots) are structurally TiO2 nanoparticles (in the order of 25 nm in diameter from commercially available colloidal TiO2 samples) surface-attached by nanoscale carbon domains with organic moieties, thus equivalent to hybrids of individual TiO2 nanoparticles each decorated with many carbon dots. These hybrid dots with exposure to visible light exhibit potent antibacterial properties, similar to those found in neat carbon dots with the same light activation. The results from the use of established scavengers for reactive oxygen species (ROS) to “quench” the antibacterial activities, an indication for shared mechanistic origins, are also similar. The findings in experiments on probing biological consequences of the antibacterial action suggest that the visible light-activated C/TiO2-Dots cause significant damage to the bacterial cell membrane, resulting in higher permeability, with the associated oxidative stress leading to lipid peroxidation, inhibit...

Research paper thumbnail of Evaluation of Commercial “Carbon Quantum Dots” Sample on Origins of Red Absorption and Emission Features

C — Journal of Carbon Research, 2019

The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optic... more The commercially acquired aqueous solution of “carbon quantum dots” sample was evaluated by optical absorption and fluorescence emission methods; in reference to aqueous dispersed small carbon nanoparticles and representative carbon dots prepared from chemical functionalization of the carbon nanoparticles. The results suggest a very low content of carbon that is associated with nanoscale carbon particles/domains in the as-supplied sample; and likely significant contamination by dye-like species/mixtures. In the absence of any information on the synthesis and history of the commercial sample, the possible cause of the contamination was illustrated by an example on similar dye formation in the one-pot carbonization synthesis of “red carbon dots” from citric acid–formamide precursor mixtures under too mild processing conditions that were insufficient for the intended carbonization. The negative impacts to the carbon dots research field by the apparent proliferation and now commercial a...

Research paper thumbnail of On the myth of “red/near-IR carbon quantum dots” from thermal processing of specific colorless organic precursors

Nanoscale Advances

The thermal processing of specific precursor mixtures under relatively mild conditions does not r... more The thermal processing of specific precursor mixtures under relatively mild conditions does not result in “red/near-IR carbon dots” as previously claimed, but instead chemical reactions for molecular chromophores of red/near-IR absorptions.

Research paper thumbnail of Carbon Dots: Zero-Dimensional Carbon Allotrope with Unique Photoinduced Redox Characteristics

ACS Omega

Carbon dots (CDots) exploit and enhance the intrinsic properties of small carbon nanoparticles. T... more Carbon dots (CDots) exploit and enhance the intrinsic properties of small carbon nanoparticles. Their optical absorptions and photoinduced redox characteristics are competitive with those of conventional semiconductor quantum dots at one end and fullerenes and other carbon nanomaterials at the other. Highlighted in this mini review are the effective photon harvesting over a broad spectral range by CDots and their subsequent excited-state charge transfer processes and interactions, which have enabled their use as sensors, for photodynamic effects, and in various energy conversion technologies.

Research paper thumbnail of Carbon Dots as Potent Antimicrobial Agents

Research paper thumbnail of Carbon dots for energy conversion applications

Journal of Applied Physics

Quantum dots (QDs), generally referring to semiconductor nanocrystals that display the quantum co... more Quantum dots (QDs), generally referring to semiconductor nanocrystals that display the quantum confinement effect, have been widely pursued for many energy conversion applications. More recently, carbon dots (CDots), which are small carbon nanoparticles with various surface passivation schemes, have been found to possess optical properties and photoinduced redox characteristics resembling those of conventional semiconductor QDs and thus are amenable to some of the same uses in energy conversions. Among the various carbon nanomaterials, fullerenes have been extensively investigated for their use as critical components in optoelectronic devices and systems. Carbon nanoparticles, representing a largely ignored nanoscale carbon allotrope, are in fact more effective in some of the same functions, which are materialized and much enhanced upon the surface passivation of the nanoparticles in CDots. In this perspective article on CDots for energy conversion applications, the optical properties and redox characteristics of CDots, including the related mechanistic framework and its relationship to the use of CDots as potent photocatalysts for the conversion of CO 2 into small organic molecules, are highlighted. Also highlighted are results from representative studies using CDots in light-emitting diodes and various solar cells to demonstrate their excellent potential for a wide range of roles in optoelectronic devices and systems. Issues and opportunities in the further development of the CDots platform and related technologies are discussed.

Research paper thumbnail of Systematic Comparison of Carbon Dots from Different Preparations—Consistent Optical Properties and Photoinduced Redox Characteristics in Visible Spectrum and Structural and Mechanistic Implications

The Journal of Physical Chemistry C

Carbon dots (CDots) are characterized by their optical properties including strong absorptions an... more Carbon dots (CDots) are characterized by their optical properties including strong absorptions and bright and colorful fluorescence emissions in the visible spectrum and by their photoinduced redox characteristics as both potent electron acceptors and donors. The reported study was for a systematic comparison of CDots from different synthetic approaches based on the use of pre-existing small carbon nanoparticles sourced from pure carbon soot versus the formation of similar nanoparticles in situ via a one-pot thermal carbonization of organic molecular precursors, emphasizing spectroscopic characterizations over the visible spectrum. The results show that the CDots prepared by the latter under sufficiently robust processing conditions are generally no different from those from the former in terms of the observed optical properties and associated photoinduced redox characteristics in the application-wise more meaningful visible spectral region, suggesting a high stability or general applicability of the defi...

Research paper thumbnail of Hybrid carbon dots platform enabling opportunities for desired optical properties and redox characteristics by-design

Chemical Physics Letters

Abstract Carbon dots (CDots) exploit unique properties of small carbon nanoparticles, which repre... more Abstract Carbon dots (CDots) exploit unique properties of small carbon nanoparticles, which represent the often under-appreciated zero-dimensional carbon allotrope. The carbon nanoparticles in CDots could be modified by a selected organic chromophore of desired strong red/near-IR absorption in the dot synthesis to obtain a specific type of hybrid CDots. The reported results show that these hybrid CDots derived from the modification of core carbon nanoparticles by selected dyes or other chromophoric species represent a highly versatile and effective platform for CDots of desired optical properties and photoinduced redox characteristics in a by-design fashion.

Research paper thumbnail of Functionalization of Carbon Nanoparticles and Defunctionalization—Toward Structural and Mechanistic Elucidation of Carbon “Quantum” Dots

The Journal of Physical Chemistry C

Small carbon nanoparticles were functionalized by low-molecular weight amino compound 3-ethoxypro... more Small carbon nanoparticles were functionalized by low-molecular weight amino compound 3-ethoxypropylamine (EPA) for ultracompact carbon dots of bright fluorescence emissions. The results from solution-phase NMR characterization support the expected dot structure of carbon nanoparticles surface-attached with EPA species. The optical properties of the EPA-carbon dots share many features with those found in carbon dots of other surface functionalities, but there is an extra absorption shoulder in the blue spectral region, into which the excitation results in much enhanced green fluorescence emissions. The EPA-carbon dots were defunctionalized by gradually removing the EPA species from the carbon nanoparticles, along with spectroscopic characterizations on the samples of different degrees of defunctionalization. The outcomes further confirm the critical role of surface functionalization in the superior optical properties of carbon dots. Results from systematic measurements of fluorescence quantum yields and d...

Research paper thumbnail of A new approach in functionalization of carbon nanoparticles for optoelectronically relevant carbon dots and beyond

Carbon

Abstract Carbon dots (CDots), generally small carbon nanoparticles with surface passivation by a ... more Abstract Carbon dots (CDots), generally small carbon nanoparticles with surface passivation by a soft corona-like layer of mostly organic species, have been actively pursued for potential applications in optoelectronics, including various functions that have been served by some popular fullerene derivatives. For the preparation of CDots, chemical functionalization of pre-processed and selected small carbon nanoparticles by organic molecules, so far mostly molecules with primary and secondary amine groups, has been an effective method. In this study, carbon nanoparticles were functionalized by N-ethylcarbazole (NEC) under microwave-assisted reaction conditions for NEC-CDots, analogous but with advantages to the CDots of surface functionalization by poly(N-vinylcarbazole) (PVK, which holds a special place in optoelectronics). NEC molecules can apparently be activated under the reaction conditions for reactive functionalities such as radicals to bind to surface carbons of the nanoparticles, consistent with the observed high stability of NEC-CDots. These dots, likely with a unique surface passivation scheme, exhibited optical properties and photoinduced redox characteristics similar to those found in other high-performance CDots. The potentially broad applicability of the new functionalization approach is discussed, so are implications of the unique surface passivation of carbon nanoparticles by the carbazole moieties.