Self-Assembled Graphene-Based Architectures and Their Applications

Photochromic Carbon Nanomaterials: An Emerging Class of Light-Driven Hybrid Functional Materials

Photochromic molecules have remarkable potential in memory and optical devices, as well as in driving and manipulating molecular motors or actuators and many other systems using light. When photochromic molecules are introduced into carbon nanomaterials (CNMs), the resulting hybrids provide unique advantages and create new functions that can be employed in specific applications and devices. This review highlights the recent developments in diverse photochromic CNMs. Photochromic molecules and CNMs are also introduced. The fundamentals of different photochromic CNMs are discussed, including design principles and the types of interactions between CNMs and photochromic molecules via covalent interactions and non-covalent bonding such as π-π stacking, amphiphilic, electrostatic, and hydrogen bonding. Then the properties of photochromic CNMs, e.g., in photopatterning, fluorescence modulation, actuation, and photoinduced surface-relief gratings, and their applications in energy storage (solar thermal fuels, photothermal batteries, and supercapacitors), nanoelectronics (transistors, molecular junctions, photo-switchable conductance, and photoinduced electron transfer), sensors, and bioimaging are highlighted. Finally, an outlook on the challenges and opportunities in the future of photochromic CNMs is presented. This review discusses a vibrant interdisciplinary research field and is expected to stimulate further developments in nanoscience, advanced nanotechnology, intelligently responsive materials, and devices.

Graphene-Based Engineered Living Materials

With the rise of engineered living materials (ELMs) as innovative, sustainable and smart systems for diverse engineering and biological applications, global interest in advancing ELMs is on the rise. Graphene-based nanostructures can serve as effective tools to fabricate ELMs. By using graphene-based materials as building units and microorganisms as the designers of the end materials, next-generation ELMs can be engineered with the structural properties of graphene-based materials and the inherent properties of the microorganisms. However, some challenges need to be addressed to fully take advantage of graphene-based nanostructures for the design of next-generation ELMs. This work covers the latest advances in the fabrication and application of graphene-based ELMs. Fabrication strategies of graphene-based ELMs are first categorized, followed by a systematic investigation of the advantages and disadvantages within each category. Next, the potential applications of graphene-based ELMs are covered. Moreover, the challenges associated with fabrication of next-generation graphene-based ELMs are identified and discussed. Based on a comprehensive overview of the literature, the primary challenge limiting the integration of graphene-based nanostructures in ELMs is nanotoxicity arising from synthetic and structural parameters. Finally, we present possible design principles to potentially address these challenges.

Design, synthesis, and application of some two-dimensional materials

Two-dimensional (2D) materials are widely used as key components in the fields of energy conversion and storage, optoelectronics, catalysis, biomedicine, etc. To meet the practical needs, molecular structure design and aggregation process optimization have been systematically carried out. The intrinsic correlation between preparation methods and the characteristic properties is investigated. This review summarizes the recent research achievements of 2D materials in the aspect of molecular structure modification, aggregation regulation, characteristic properties, and device applications. The design strategies to fabricate functional 2D materials starting from precursor molecules are introduced in detail referring to organic synthetic chemistry and self-assembly technology. It provides important research ideas for the design and synthesis of related materials.

On the Road to the Frontiers of Lithium-Ion Batteries: A Review and Outlook of Graphene Anodes

Graphene has long been recognized as a potential anode for next-generation lithium-ion batteries (LIBs). The past decade has witnessed the rapid advancement of graphene anodes, and considerable breakthroughs are achieved so far. In this review, the aim is to provide a research roadmap of graphene anodes toward practical LIBs. The Li storage mechanism of graphene is started with and then the approaches to improve its electrochemical performance are comprehensively summarized. First, morphologically engineered graphene anodes with porous, spheric, ribboned, defective and holey structures display improved capacity and rate performance owing to their highly accessible surface area, interconnected diffusion channels, and sufficient active sites. Surface-modified graphene anodes with less aggregation, fast electrons/ions transportation, and optimal solid electrolyte interphase are discussed, demonstrating the close connection between the surface structure and electrochemical activity of graphene. Second, graphene derivatives anodes prepared by heteroatom doping and covalent functionalization are outlined, which show great advantages in boosting the Li storage performances because of the additionally introduced defect/active sites for further Li accommodation. Furthermore, binder-free and free-standing graphene electrodes are presented, exhibiting great prospects for high-energy-density and flexible LIBs. Finally, the remaining challenges and future opportunities of practically available graphene anodes for advanced LIBs are highlighted.

Self-assembly of guanosine into carbon-based multilayer materials

We report the utilization of guanosine as a supramolecular precursor that unprecedentedly renders the formation of carbon-based multilayer materials with naturally high-level nitrogen doping. As a proof-of-concept, the porous carbon multilayers after anchoring 0.5 wt% Rh electrocatalysts displayed an excellent hydrogen evolution reaction activity.

Applications of Graphene in Five Senses, Nervous System, and Artificial Muscles

Graphene remains of great interest in biomedical applications because of biocompatibility. Diseases relating to human senses interfere with life satisfaction and happiness. Therefore, the restoration by artificial organs or sensory devices may bring a bright future by the recovery of senses in patients. In this review, we update the most recent progress in graphene based sensors for mimicking human senses such as artificial retina for image sensors, artificial eardrums, gas sensors, chemical sensors, and tactile sensors. The brain-like processors are discussed based on conventional transistors as well as memristor related neuromorphic computing. The brain-machine interface is introduced for providing a single pathway. Besides, the artificial muscles based on graphene are summarized in the means of actuators in order to react to the physical world. Future opportunities remain for elevating the performances of human-like sensors and their clinical applications.

The Role of Oxidation Pattern and Water Content in the Spatial Arrangement and Dynamics of Oxidized Graphene-Based Aqueous Dispersions

In this work, we employ fully atomistic molecular dynamics simulations to elucidate the effects of the oxidation pattern and of the water content on the organization of graphene sheets in aqueous dispersions and on the dynamic properties of the different moieties at neutral pH conditions. Analysis of the results reveals the role of the oxidation motif (peripherally or fully oxidized flakes) in the tendency of the flakes to self-assemble and in the control of key structural characteristics, such as the interlayer distance between the sheets and the average size and the distribution of the formed aggregates. In certain cases, the results are compared to a pertinent experimental system, validating further the relevant computational models. Examination of the diffusional motion of the oxidized flakes shows that different degrees of spatial restriction are imposed upon the decrease in the water content and elucidates the conditions under which a motional arrest of the flakes takes place. At constant water content, the structural differences between the formed aggregates appear to additionally impart distinct diffusional characteristics of a water molecule. A detailed examination of the counterion dynamics describes their interaction with the oxidized flakes and their dependence on the water content and on the oxidation pattern, offering new insight into the expected electrical properties of the dispersions. The detailed information provided by this work will be particularly useful in applications such as molecular sieving, nanofiltration, and in cases where conductive membranes based on oxidized forms of graphene are used.

Effects of oppositely charged moieties on the self-assembly and biophysicochemical properties of polyurethane micelles

Gemini quaternary ammonium (GQA), a type of cationic surfactant, exhibits excellent micellization ability and acts as a cell internalization promoter to increase the permeability of the cell membrane. GQA is sensitive to ionic solutions, which disturb its stabilization and leads to the rapid degradation of its polymer micelles due to its unique hydrophilic N⁺ structure. However, the effect of negatively charged moieties in the polymer chains of GQA on its action in polymer micelles, typically with regard to its micellization and biological performance, remains unclear. In this work, a series of polyurethane micelles containing various ratios of oppositely charged moieties was prepared. We found that the interchain electrostatic interaction severely undermines the function of the GQA surfactant and hinders the self-assembly and stabilization of polyurethane micelles. Specifically, a hydrophilic corona with a longer length cannot completely overcome this effect. By regulating the ratio of oppositely charged moieties, micelles exhibited tunable biological properties, such as biocompatibility, cytotoxicity, cell internalization, and phagocytosis by macrophages. Based on our results, a moderate molecular weight of mPEG (Mn = 1900) and a slight positive surface potential (∼10 mV) are the best surface parameters for the comprehensive performance of the studied nanoplatforms. This study provides a further understanding of the electrostatic interaction effect on the properties of the cationic GQA, offering rational guidance for the design and fabrication of GQA polymer micelles.

Self-assembly of graphene oxide flakes for smart and multifunctional coating with reversible formation of wrinkling patterns

One of the main purposes of smart and multifunctional coatings is to have the versatility to be applied in a wide range of applications. However, the functions of smart materials are often highly limited. In particular, the stimuli-responsive lateral expansion of coatings based on 2D materials has not been reported before. This manuscript describes small two-dimensional graphene oxide (GO) flakes (e.g., thin sheets with a thickness of a few nanometers and much larger lateral dimensions) that act as elementary agents for the formation of smart and multifunctional coatings. The coating can be self-assembled from the GO flakes and disassembled flexibly when required. The coating is stimuli-responsive: upon localized contact with water, it expands and forms wrinkling patterns throughout its whole surface. Evaporating the water allows the wrinkles to disappear; hence, the process is reversible. This stimuli-responsiveness can be controlled to be reduced or completely switched off by temperature or pressure. These features are fundamentally due to the reversible intermolecular interactions among the flakes and favorable packing structure of the coating. The smart coating is shown to be useful for patterned fluidic systems of the desired shapes and the development of channels between fluidic reservoirs via the shortest path. Importantly, these results showed that a simple collection of uniquely 2D elementary agents with small nanoscale thickness can self-assemble into macroscopic materials that perform interactive and multifunctional operations.

3D graphene-based adsorbents: Synthesis, proportional analysis and potential applications in oil elimination

The suitability and efficacy of three-dimensional (3D) graphene, including its derivatives, have garnered widespread attention towards the development of novel, sustainable materials with ecological amenability. This is especially relevant towards its utilization as adsorbents of wastewater contaminants, such as heavy metals, dyes, and oil, which could be majorly attributed to its noteworthy physicochemical features, particularly elevated chemical and mechanical robustness, advanced permeability, as well as large specific surface area. In this review, we emphasize on the adsorptive elimination of oil particles from contaminated water. Specifically, we assess and collate recent literature on the conceptualization and designing stages of 3D graphene-based adsorbents (3DGBAs) towards oil adsorption, including their applications in either batch or continuous modes. In addition, we analytically evaluate the adsorption mechanism, including sorption sites, physical properties, surface chemistry of 3DGBA and interactions between the adsorbent and adsorbate involving the adsorptive removal of oil, as well as numerous effects of adsorption conditions on the adsorption performance, i.e. pH, temperature, initial concentration of oil contaminants and adsorbent dosage. Furthermore, we focus on the equilibrium isotherms and kinetic studies, in order to comprehend the oil elimination procedures. Lastly, we designate encouraging avenues and recommendations for a perpetual research thrust, and outline the associated future prospects and perspectives.

An Update on Graphene-Based Nanomaterials for Neural Growth and Central Nervous System Regeneration

Thanks to their reduced size, great surface area, and capacity to interact with cells and tissues, nanomaterials present some attractive biological and chemical characteristics with potential uses in the field of biomedical applications. In this context, graphene and its chemical derivatives have been extensively used in many biomedical research areas from drug delivery to bioelectronics and tissue engineering. Graphene-based nanomaterials show excellent optical, mechanical, and biological properties. They can be used as a substrate in the field of tissue engineering due to their conductivity, allowing to study, and educate neural connections, and guide neural growth and differentiation; thus, graphene-based nanomaterials represent an emerging aspect in regenerative medicine. Moreover, there is now an urgent need to develop multifunctional and functionalized nanomaterials able to arrive at neuronal cells through the blood-brain barrier, to manage a specific drug delivery system. In this review, we will focus on the recent applications of graphene-based nanomaterials in vitro and in vivo, also combining graphene with other smart materials to achieve the best benefits in the fields of nervous tissue engineering and neural regenerative medicine. We will then highlight the potential use of these graphene-based materials to construct graphene 3D scaffolds able to stimulate neural growth and regeneration in vivo for clinical applications.

Principles governing control of aggregation and dispersion of aqueous graphene oxide

Controlling the structure of graphene oxide (GO) phases and their smaller analogues, graphene (oxide) quantum dots (GOQDs), is vitally important for any of their widespread intended applications: highly ordered arrangements of nanoparticles for thin-film or membrane applications of GO, dispersed nanoparticles for composite materials and three-dimensional porous arrangements for hydrogels. In aqueous environments, it is not only the chemical composition of the GO flakes that determines their morphologies; external factors such as pH and the coexisting cations also influence the structures formed. By using accurate models of GO that capture the heterogeneity of surface oxidation and very large-scale coarse-grained molecular dynamics that can simulate the behaviour of GO at realistic sizes of GOQDs, the driving forces that lead to the various morphologies in aqueous solution are resolved. We find the morphologies are determined by a complex interplay between electrostatic, [Formula: see text]-[Formula: see text] and hydrogen bonding interactions. Assembled morphologies can be controlled by changing the degree of oxidation and the pH. In acidic aqueous solution, the GO flakes vary from fully aggregated over graphitic domains to partial aggregation via hydrogen bonding between hydroxylated domains, leading to the formation of planar extended flakes at high oxidation ratios and stacks at low oxidation ratios. At high pH, where the edge carboxylic acid groups are deprotonated, electrostatic repulsion leads to more dispersion, but a variety of aggregation behaviour is surprisingly still observed: over graphitic regions, via hydrogen bonding and "face-edge" interactions. Calcium ions cause additional aggregation, with a greater number of "face-face" and "edge-edge" aggregation mechanisms, leading to irregular aggregated structures. "Face-face" aggregation mechanisms are enhanced by the GO flakes possessing distinct domains of hydroxylated and graphitic regions, with [Formula: see text]-[Formula: see text] and hydrogen bonding interactions prevalent between these regions on aggregated flakes respectively. These findings furnish explanations for the aggregation characteristics of GO and GOQDs, and provide computational methods to design directed synthesis routes for self-assembled and associated applications.

Biomimetic Graphene/Spongin Scaffolds for Improved Osteoblasts Bioactivity via Dynamic Mechanical Stimulation

Biomimetics offers excellent prospects for design a novel generation of improved biomaterials. Here the controlled integration of graphene oxide (GO) derivatives with a 3D marine spongin (MS) network is explored to nanoengineer novel smart bio-based constructs for bone tissue engineering. The results point out that 3D MS surfaces can be homogeneously coated by layer-by-layer (LbL) assembly of oppositely charged polyethyleneimine (PEI) and GO. Notably, the GOPEI@MS bionanocomposites present a high structural and mechanical stability under compression tests in wet conditions (shape memory). Dynamic mechanically (2 h of sinusoidal compression cyclic interval (0.5 Hz, 0-10% strain)/14 d) stimulates GOPEI@MS seeded with osteoblast (MC3T3-E1), shows a significant improvement in bioactivity, with cell proliferation being two times higher than under static conditions. Besides, the dynamic assays show that GOPEI@MS bionanocomposites are able to act as mechanical stimulus-responsive scaffolds able to resemble physiological bone extracellular matrix (ECM) requirements by strongly triggering mineralization of the bone matrix. These results prove that the environment created by the system cell-GOPEI@MS is suitable for controlling the mechanisms regulating mechanical stimulation-induced cell proliferation for potential in vivo experimentation.

Recent Progress in Superhydrophilic Carbon-Based Composite Membranes for Oil/Water Emulsion Separation

The purification of stabilized oil/water emulsions is essential to meet the ever increasing demand for monitoring water in the environment, which has been addressed with superwetting carbon-based separation membranes. These include superhydrophilic carbon-based membranes whose progress in recent years and perspectives are reviewed in this paper. The membrane construction strategy is organized into four parts, vacuum-assisted self-assembly, sol-gel process, electrospinning, and vacuum-assisted filtration. In each section, the design strategies and their responding disadvantages have been comprehensively discussed. The challenges and prospects concerning the superhydrophilic carbon-based separation membranes for oily wastewater purification are also summarized to arouse researchers to carry out more studies.

Roles of Graphene Oxide in Heterogeneous Photocatalysis

Graphene oxide (GO) has been widely utilized as the precursor of graphene (GR) to fabricate GR-based hybrid photocatalysts for solar-to-chemical energy conversion. However, until now, the properties and roles that GO played in heterogeneous photocatalysis have remained relatively elusive. In this Review, we start with a brief discussion of synthesis and structure of GO. Then, the photocatalysis-related properties of GO, including electrical conductivity, surface chemistry, dispersibility, and semiconductor properties, are concisely summarized. In particular, we have highlighted the fundamental multifaceted roles of GO in heterogeneous photocatalysis, which contain the precursor of GR, cross-linked framework for constructing aerogel photocatalyst, macromolecular surfactant, two-dimensional growth template, and photocatalyst by itself. Furthermore, the future prospects and remaining challenges on developing effective GO-derived hybrid photocatalysts are presented, which is expected to inspire further research into this promising research domain.

Recent advances in graphene-based nanobiosensors for salivary biomarker detection

As biosensing research is rapidly advancing due to significant developments in materials, chemistry, and electronics, researchers strive to build cutting-edge biomedical devices capable of detecting health-monitoring biomarkers with high sensitivity and specificity. Biosensors using nanomaterials are highly promising because of the wide detection range, fast response time, system miniaturization, and enhanced sensitivity. In the recent development of biosensors and electronics, graphene has rapidly gained popularity due to its superior electrical, biochemical, and mechanical properties. For biomarker detection, human saliva offers easy access with a large variety of analytes, making it a promising candidate for its use in point-of-care (POC) devices. Here, we report a comprehensive review that summarizes the most recent graphene-based nanobiosensors and oral bioelectronics for salivary biomarker detection. We discuss the details of structural designs of graphene electronics, use cases of salivary biomarkers, the performance of existing sensors, and applications in health monitoring. This review also describes current challenges in materials and systems and future directions of the graphene bioelectronics for clinical POC applications. Collectively, the main contribution of this paper is to deliver an extensive review of the graphene-enabled biosensors and oral electronics and their successful applications in human salivary biomarker detection.

An upgraded electro-Fenton treatment of wastewater using nanoclay-embedded graphene composite prepared via exfoliation of pencil rods by submerged liquid plasma

In this work, two types of electrochemical electrodes were synthesized using two types (i.e., 4 black (4B) and hard black (HB)) of pencil rods during submerged liquid plasma (SLP) process. At high potential (3 kV) electrons, the SLP process offered an effective exfoliation route for the disorientation of the graphite sp² domain to produce two nanoclay-graphene composite electrodes with a few graphene layers (thickness = 4-9 layers) and high dispersibility (< 19% settlement: 4 h) in polar/non-polar solution (52-53.1% settlement: 4 h). Their performance was then evaluated towards the electro-Fenton (EF) degradation of lindane using a coated Fe₃O₄ plate (as Fenton catalyst). Accordingly, both 4B- and HB-ENcGe electrodes showed high specific capacitance values (473 and 363 F g^-1) at 0.05 A g^-1 and excellent triangular charge-discharge patterns (< 9% and 35% reduction of capacitance, respectively after 1000 cycles (charging rate: 0.2 A g^-1)). At pH 3 and current density of 6.5 mA cm^-2, 4B-ENcGe exhibited superior EF degradation performance (99.4% after 60 min) against 2.5 mg L^-1 lindane (H₂O₂ generation capacity: 2.53 mmol. h^-1, current efficiency: 89.4%, and stability: up to 5th cycles). The complete EF-based mineralization of lindane suggests that these electrodes should offer one-step cost-effective treatment for wastewater contaminants.

From 2D Graphene Nanosheets to 3D Graphene-based Macrostructures

The combination of exceptional functionalities offered by 3D graphene-based macrostructures (GBMs) has attracted tremendous interest. 2D graphene nanosheets have a high chemical stability, high surface area and customizable porosity, which was extensively researched for a variety of applications including CO₂ adsorption, water treatment, batteries, sensors, catalysis, etc. Recently, 3D GBMs have been successfully achieved through few approaches, including direct and non-direct self-assembly methods. In this review, the possible routes used to prepare both 2D graphene and interconnected 3D GBMs are described and analyzed regarding the involved chemistry of each 2D/3D graphene system. Improvement of the accessible surface of 3D GBMs where the interface exchanges are occurring is of great importance. A better control of the chemical mechanisms involved in the self-assembly mechanism itself at the nanometer scale is certainly the key for a future research breakthrough regarding 3D GBMs.

Graphene-Based Macromolecular Assemblies for Scavenging Heavy Metals

The integration of graphene or graphene oxide nanosheets into three-dimensional (3D) graphene-based macromolecular assemblies (GMAs), in the form of sponges, beads, fibres, films, and crumpled nanosheets, has greatly advanced their environmental remediation applications. This is attributed to the outstanding physicochemical characteristics and superlative mechanical features of 3D GMAs, including precise and physically linked permeable networks, enormous surface area, profound porosity, and high-class sturdiness, amongst others. In this review, the recent advancements towards the exploration of 3D GMAs as an exciting new class of high-performance adsorbents, for eliminating toxic heavy metal ions from both wastewater and freshwater, are systematically summarized and discussed, from both fundamental and applied perspectives. In particular, the numerous surface modification techniques that are actively pursued to enrich the metal adsorption capacity of 3D GMAs, are comprehensively examined. Additionally, associated challenges are pointed out and tactical research strategies and improvements are proposed, with an eye on the conceivable future.

Hexylsulfanyl-substituted CoPc and GO-CoPc on Ni foam as electroactive material for supercapacitors

For energy storage applications, hexylsulfanyl-substituted CoPc and GO-CoPc electrodes were prepared on Ni foam, and then electrochemical properties of the materials were investigated. The GO-CoPc nanocomposite electrode exhibits 56 mFcm[Formula: see text] at 1.4 mAcm[Formula: see text] current density. The results show that the GO-CoPc nanocomposite electrode is a promising electroactive material for supercapacitors.

Self-Assembled Functionally Graded Graphene Films with Tunable Compositions and Their Applications in Transient Electronics and Actuation

The facile fabrication of functionally graded all-graphene films using a single-step casting process is reported. The films consist of a self-assembled graphene oxide (GO) precursor that can be reduced to different levels on an active metal substrate. Control of processing conditions such as the underlying substrate metal and the film-drying environment results in an ability to tailor the internal architecture of the films as well as to functionally grade the reduction of GO. A gradient arrangement within each film, where one side is electrically conductive reduced GO (rGO) and the other side is insulating GO, was confirmed by scanning electron microscopy, Raman, X-ray diffraction, Fourier transform infrared, and X-ray photoelectron spectroscopy characterization studies. All-graphene-based freestanding films with selectively reduced GO were used in transient electronic applications such as flexible circuitry and RFID tag antennas, where their decommissioning is easily achieved by capitalizing on GO's ability to readily dissociate and create a stable suspension in water. Furthermore, the functionally graded structure was found to exhibit differential swelling behavior, and its potential applications in graphene-based actuators are outlined.

Catalytic use of layered materials for fine chemical syntheses

The present work reviews the catalytic use of layered solid materials for fine chemical syntheses with focus on layered double hydroxides, but including other classes of layered compounds of catalytic relevance.

In Situ Activating Strategy to Significantly Boost Oxygen Electrocatalysis of Commercial Carbon Cloth for Flexible and Rechargeable Zn-Air Batteries

An in situ strategy to simultaneously boost oxygen reduction and oxygen evolution (ORR/OER) activities of commercial carbon textiles is reported and the direct use of such ubiquitous raw material as low-cost, efficient, robust, self-supporting, and bifunctional air electrodes in rechargeable Zn-air batteries is demonstrated. This strategy not only furnishes carbon textiles with a large surface area and hierarchical meso-microporosity, but also enables efficient dual-doping of N and S into carbon skeletons while retaining high conductivity and stable monolithic structures. Thus, although original carbon textile has rather poor catalytic activity, the activated textiles without loading other active materials yield effective ORR/OER bifunctionality and stability with a much lower reversible overpotential (0.87 V) than those of Pt/C (1.10 V) and RuO2 (1.02 V) and many reported metal-free bifunctional catalysts. Importantly, they can concurrently function as current collectors and as ORR/OER catalysts for rechargeable aqueous and flexible solid-state Zn-air batteries, showing excellent cell performance, long lifetime, and high flexibility.

Morphology-Controlled Aluminum-Doped Zinc Oxide Nanofibers for Highly Sensitive NO2 Sensors with Full Recovery at Room Temperature

Room-temperature (RT) gas sensitivity of morphology-controlled free-standing hollow aluminum-doped zinc oxide (AZO) nanofibers for NO2 gas sensors is presented. The free-standing hollow nanofibers are fabricated using a polyvinylpyrrolidone fiber template electrospun on a copper electrode frame followed by radio-frequency sputtering of an AZO thin overlayer and heat treatment at 400 °C to burn off the polymer template. The thickness of the AZO layer is controlled by the deposition time. The gas sensor based on the hollow nanofibers demonstrates fully recoverable n-type RT sensing of low concentrations of NO2 (0.5 ppm). A gas sensor fabricated with Al2O3-filled AZO nanofibers exhibits no gas sensitivity below 75 °C. The gas sensitivity of a sensor is determined by the density of molecules above the minimum energy for adsorption, collision frequency of gas molecules with the surface, and available adsorption sites. Based on finite-difference time-domain simulations, the RT sensitivity of hollow nanofiber sensors is ascribed to the ten times higher collision frequency of NO2 molecules confined inside the fiber compared to the outer surface, as well as twice the surface area of hollow nanofibers compared to the filled ones. This approach might lead to the realization of RT sensitive gas sensors with 1D nanostructures.