Three-dimensional mesoporous graphene aerogel-supported SnO2 nanocrystals for high-performance NO2 gas sensing at low temperature

Hierachical Aerogel-Supported Cu-Sn-Ox Solid Solutions for Highly Selective CO2 Electroreduction and Zn-CO2 Batteries

The electrochemical CO2 reduction reaction (CO2RR) into high-value carbon compounds such as CO and HCOOH is a promising strategy for the utilization and conversion of emitted CO2. However, the selectivity of the CO2RR for HCOOH is typically less than 90% and operates within a narrow voltage range, which limits its practical application. Herein, we propose a novel heterostructural aerogel as a highly efficient electrocatalyst for CO2RR to HCOOH. This catalyst consists of Cu-Sn-Ox solid solutions embedded in a reduced graphene oxide matrix (Cu-Sn-Ox/rGO). The incorporation of Cu2+ into the SnO2 matrix enhances HCOOH production by improving the adsorption of the *OCHO intermediate and inhibiting H2 evolution, as confirmed by in situ measurements and computational studies. As a result, Cu-Sn-Ox/rGO achieves a remarkable Faradaic efficiency (FE) of up to 91.4% for HCOOH and maintains high selectivity over a broad operating voltage range (-0.8 to -1.1 V). Additionally, the assembled Zn-CO2 batteries demonstrated an excellent power density of 1.14 mW/cm2 and exceptional stability for over 25 h.

Microwave-Solvothermal Synthesis of Mesoporous CeO2/CNCs Nanocomposite for Enhanced Room Temperature NO2 Detection

Nitrogen dioxide (NO2) gas sensors are pivotal in upholding environmental integrity and human health, necessitating heightened sensitivity and exceptional selectivity. Despite the prevalent use of metal oxide semiconductors (MOSs) for NO2 detection, extant solutions exhibit shortcomings in meeting practical application criteria, specifically in response, selectivity, and operational temperatures. Here, we successfully employed a facile microwave-solvothermal method to synthesize a mesoporous CeO2/CNCs nanocomposite. This methodology entails the rapid and comprehensive dispersion of CeO2 nanoparticles onto helical carbon nanocoils (CNCs), resulting in augmented electronic conductivity and an abundance of active sites within the composite. Consequently, the gas-sensing sensitivity of the nanocomposite at room temperature experienced a notable enhancement. Moreover, the presence of cerium oxide and the conversion of Ce3+ and Ce4+ ions facilitated the generation of oxygen vacancies in the composites, thereby further amplifying the sensing performance. Experimental outcomes demonstrate that the nanocomposite exhibited an approximate 9-fold increase in response to 50 ppm NO2 in comparison to pure CNCs at room temperature. Additionally, the CeO2/CNCs sensor displayed remarkable selectivity towards NO2 when exposed to gases such as NH3, CO, SO2, CO2, and C2H5OH. This straightforward microwave-solvothermal method presents an appealing strategy for the research and development of intelligent sensors based on CNCs nanomaterials.

Facile fabrication of laser induced versatile graphene-metal nanoparticles electrodes for the detection of hazardous molecules

In this work, we developed a facile method to fabricate laser induced versatile graphene-metal nanoparticles (LIG-MNPs) electrodes with redox molecules sensing capabilities. Unlike conventional post-electrodes deposition, versatile graphene-based composites were engraved by a facile synthesis process. As a general protocol, we successfully prepared modular electrodes including LIG-PtNPs and LIG-AuNPs and applied them to electrochemical sensing. This facile laser engraving process enables rapid preparation and modification of electrodes, as well as simple replacement of metal particles modification towards varied sensing targets. The LIG-MNPs showed high sensitivity towards H₂O₂ and H₂S due to their excellent electron transmission efficiency and electrocatalytic activity. By simply changing the types of coated precursors, the LIG-MNPs electrodes have successfully achieved real-time monitoring of H₂O₂ released from tumor cells and H₂S contained in wastewater. This work contributed a universal and versatile protocol for quantitatively detecting a wide range of hazardous redox molecules.

Application of Titanium Carbide MXenes in Chemiresistive Gas Sensors

The titanium carbide MXenes currently attract an extreme amount of interest from the material science community due to their promising functional properties arising from the two-dimensionality of these layered structures. In particular, the interaction between MXene and gaseous molecules, even at the physisorption level, yields a substantial shift in electrical parameters, which makes it possible to design gas sensors working at RT as a prerequisite to low-powered detection units. Herein, we consider to review such sensors, primarily based on Ti3C2Tx and Ti2CTx crystals as the most studied ones to date, delivering a chemiresistive type of signal. We analyze the ways reported in the literature to modify these 2D nanomaterials for (i) detecting various analyte gases, (ii) improving stability and sensitivity, (iii) reducing response/recovery times, and (iv) advancing a sensitivity to atmospheric humidity. The most powerful approach based on designing hetero-layers of MXenes with other crystals is discussed with regard to employing semiconductor metal oxides and chalcogenides, noble metal nanoparticles, carbon materials (graphene and nanotubes), and polymeric components. The current concepts on the detection mechanisms of MXenes and their hetero-composites are considered, and the background reasons for improving gas-sensing functionality in the hetero-composite when compared with pristine MXenes are classified. We formulate state-of-the-art advances and challenges in the field while proposing some possible solutions, in particular via employing a multisensor array paradigm.

Studies on nanomaterial-based p-type semiconductor gas sensors

The development of various metal oxide semiconductor materials has resulted in better performance of the gas sensors in terms of selectivity, sensitivity, and response time. Different types of nanostructured materials, i.e., 2D materials, carbon nanotubes, and metal oxides, are used in the gas sensing applications. Generally, the metal oxide-based gas sensor operates at higher temperature to activate the adsorption process between the material surface and the target gas. The higher operating temperature of the gas sensor leads to more power consumption and produces defects in the grain boundary of metal oxide. To improve the selectivity and minimize the power consumption, nanoparticle-based p-type semiconductor materials are being developed. P-type metal oxide-based semiconductor materials have the ability to produce a hole accumulation layer which can chemisorb the oxygen molecules of higher concentration and these materials are not affected by humidity. The structure of p-type nanomaterial-based gas sensor depends upon the fabrication techniques which can affect the sensing properties of semiconductor materials. The hole accumulation layer is also known as conduction layer which is developed in the outer shell of p-type semiconductor material and the sensing mechanism is controlled by grain boundaries which is different from the n-type semiconductor material. This paper reviews the preparation methods, morphological analysis, and sensing mechanisms of nanomaterial-based p-type metal oxide-based gas sensors.

High-Performance Ppb Level NO2 Gas Sensor Based on Colloidal SnO2 Quantum Wires/Ti3C2Tx MXene Composite

Nitrogen dioxide is one origin of air pollution from fossil fuels with the potential to cause great harm to human health in low concentrations. Therefore, low-cost, low-power-consumption sensors for low-concentration NO₂ detection are essential. Herein, heterojunction by SnO₂ quantum wires, a traditional metal oxide NO₂ sensing material, and Ti₃C₂T_x MXene, a novel type of 2D layered material, was synthesized using a simple solvothermal method for enhancing gas-sensing performance and reducing operating temperature. The operating temperature was reduced to 80 °C, with a best performance of 27.8 and a fast response and recovery time (11 s and 23 s, respectively). The SnO₂ and Ti₃C₂T_x MXene composite exhibits high speed and low detection limit due to the construction of the heterojunction with high conductive Ti₃C₂T_x MXene. The selectivity and stability of gas sensors are carried out. This could enable the realization of fast response, high-sensitivity, and selective NO₂ sensing under low operating temperatures.

Environmental gas sensors based on electroactive hybrid organic-inorganic nanocomposites using nanostructured materials

Advanced gas sensing devices are urgently demanded in the modern scientific world to control air pollution and protect human life. For this purpose, semiconducting electroactive materials can revolutionize the idea of conventional gas sensors. Chemi-resistive gas sensors based on electroactive hybrid organic-inorganic nanocomposites are incredibly promising gas sensing materials because they possess the advantages of excellent selectivity, high sensitivity, low response time, repeatability, high stability, cost-effectiveness, and simple fabrication techniques, and they can be operated at room temperature. This review emphasizes the recent developments of organic-inorganic hybrid nanocomposite-based electroactive gas sensors, including metal oxide nanocomposites, which are potential gas sensing materials due to the presence of numerous charge carriers. The review also focuses on nanostructured materials of different dimensions, such as semiconducting quantum dots, carbon dots, nanotubes, nanowires, and nanosheets, used for developing these gas sensing compounds and their significance and challenges. Some possible fabrication techniques for developing efficient gas sensors with different morphologies are discussed, with their probable sensing mechanism behind the detection of toxic vapours. Subsequently, a summary and possible outcome of this study, along with the various achievements and prospects in this field, are also discussed.

Tin Oxide (SnO2)-Decorated Reduced Graphene Oxide (rGO)-Based Hydroelectric Cells to Generate Large Current

Nonphotocatalytic water splitting through oxygen-deficient, mesoporous metal oxide design-based hydroelectric cells (HECs) is a well-known phenomenon. To exploit more power from HECs, a metal oxide with more oxygen deficiency is desirable. In this study, oxygen-deficient mesoporous SnO2 via a sol-gel method and its composites with reduced graphene oxide (rGO) have been presented. Raman spectra of SnO2-rGO nanocomposites revealed an increase in the oxygen vacancies, while the X-ray diffraction (XRD) pattern confirmed the strain formation in the nanocomposite lattice owing to defect formation. The X-ray photoemission spectroscopy (XPS) results also indicated the presence of oxygen vacancies on the surface of SnO2, whereas Brunauer-Emmett-Teller (BET) measurements revealed that adding rGO into SnO2 increased the surface area from 44.54 to 84.00 m2 g-1. The water molecules are chemidissociated on the oxygen-deficient mesoporous surface of the pellet followed by physiodissociation at the mesopores. The redox reaction of the dissociated ions at the Zn anode and the Ag inert cathode produces current in the outer circuit. Interestingly, adding few drops of water into a SnO2-rGO-based HEC resulted in a short-circuit current of 148 mA with an open-cell voltage of 1.0 V. The maximum power delivered by the SnO2-rGO-based HEC is 148 mW. The addition of rGO into SnO2 boosts the peak current remarkably from 68 to 148 mA, which is the highest reported current generated by a hydroelectric cell.

Mechanisms of NO2 Detection in Hybrid Structures Containing Reduced Graphene Oxide: A Review

The sensitive detection of harmful gases, in particular nitrogen dioxide, is very important for our health and environment protection. Therefore, many papers on sensor materials used for NO₂ detection have been published in recent years. Materials based on graphene and reduced graphene oxide deserve special attention, as they exhibit excellent sensor properties compared to the other materials. In this paper, we present the most recent advances in rGO hybrid materials developed for NO₂ detection. We discuss their properties and, in particular, the mechanism of their interaction with NO₂. We also present current problems occuring in this field.

Heterojunctions of rGO/Metal Oxide Nanocomposites as Promising Gas-Sensing Materials-A Review

Monitoring environmental hazards and pollution control is vital for the detection of harmful toxic gases from industrial activities and natural processes in the environment, such as nitrogen dioxide (NO2), ammonia (NH3), hydrogen (H2), hydrogen sulfide (H2S), carbon dioxide (CO2), and sulfur dioxide (SO2). This is to ensure the preservation of public health and promote workplace safety. Graphene and its derivatives, especially reduced graphene oxide (rGO), have been designated as ideal materials in gas-sensing devices as their electronic properties highly influence the potential to adsorb specified toxic gas molecules. Despite its exceptional sensitivity at low gas concentrations, the sensor selectivity of pristine graphene is relatively weak, which limits its utility in many practical gas sensor applications. In view of this, the hybridization technique through heterojunction configurations of rGO with metal oxides has been explored, which showed promising improvement and a synergistic effect on the gas-sensing capacity, particularly at room temperature sensitivity and selectivity, even at low concentrations of the target gas. The unique features of graphene as a preferential gas sensor material are first highlighted, followed by a brief discussion on the basic working mechanism, fabrication, and performance of hybridized rGO/metal oxide-based gas sensors for various toxic gases, including NO2, NH3, H2, H2S, CO2, and SO2. The challenges and prospects of the graphene/metal oxide-based based gas sensors are presented at the end of the review.

The Recent Development in Chemoresistive-Based Heterostructure Gas Sensor Technology, Their Future Opportunities and Challenges: A Review

Atmospheric pollution has become a critical problem for modern society; therefore, the research in this area continually aims to develop a high-performance gas sensor for health care and environmental safety. Researchers have made a significant contribution in this field by developing highly sensitive sensor-based novel selective materials. The aim of this article is to review recent developments and progress in the selective and sensitive detection of environmentally toxic gases. Different classifications of gas sensor devices are discussed based on their structure, the materials used, and their properties. The mechanisms of the sensing devices, identified by measuring the change in physical property using adsorption/desorption processes as well as chemical reactions on the gas-sensitive material surface, are also discussed. Additionally, the article presents a comprehensive review of the different morphologies and dimensions of mixed heterostructure, multilayered heterostructure, composite, core-shell, hollow heterostructure, and decorated heterostructure, which tune the gas-sensing properties towards hazardous gases. The article investigates in detail the growth and interface properties, concentrating on the material configurations that could be employed to prepare nanomaterials for commercial gas-sensing devices.

Electrostatic interaction-controlled dispersion of carbon nanotubes in a ternary composite for high-performance supercapacitors

Effective dispersion of carbon nanotubes (CNTs) is of great importance to achieve their intrinsic performance. Normally, it is believed that CNT dispersion is decided by interactions between CNTs and their dispersants, while other interactions are often neglected. Herein, three ionic surfactants, sodium dodecyl sulfate (SDS), dodecyl dimethyl betaine (BS-12) and cetyltrimethylammonium bromide (CTAB), are used to disperse CNTs in a ternary composite, i.e., poly(p-phenylenediamine)-phosphomolybdic acid@reduced graphene oxide (DMoG), respectively, leading to three different DMoGC composites. It has been found that the CNT dispersion in DMoGC was mainly controlled by electrostatic interactions between the surfactants and DMoG, which further exerted vital influences on the constitution, content, morphology, porous structure and supercapacitive performance of the DMoGC composites. Among the three surfactants, cationic CTAB showed the best CNT dispersion, while amphoteric BS-12 could hardly disperse CNTs in DMoGC, leading to DMoGC-CTAB with a 2 times larger specific surface area (152.3 m² g^-1) and 1.5 times higher specific capacitance (422 F g^-1) than those of DMoGC-(BS-12). Our study can provide valuable guidelines for selecting/designing effective dispersants to prepare multi-component composites containing uniformly dispersed CNTs.

Porous Pb-Doped ZnO Nanobelts with Enriched Oxygen Vacancies: Preparation and Their Chemiresistive Sensing Performance

Among various approaches to improve the sensing performance of metal oxide, the metal-doped method is perceived as effective, and has received great attention and is widely investigated. However, it is still a challenge to construct heterogeneous metal-doped metal oxide with an excellent sensing performance. In the present study, porous Pb-doped ZnO nanobelts were prepared by a simply partial cation exchange method, followed by in situ thermal oxidation. Detailed characterization confirmed that Pb was uniformly distributed on porous nanobelts. Additionally, it occupied the Zn situation, not forming its oxides. The gas-sensing measurements revealed that 0.61 at% Pb-doped ZnO porous nanobelts exhibited a selectively enhanced response with long-term stability toward n-butanol among the investigated VOCs. The relative response to 50 ppm of n-butanol was up to 47.7 at the working temperature of 300 °C. Additionally, the response time was short (about 5 s). These results were mainly ascribed to the porous nanostructure, two-dimensional belt-like morphology, enriched oxygen vacancies and the specific synergistic effect from the Pb dopant. Finally, a possible sensing mechanism of porous Pb-doped ZnO nanobelts is proposed and discussed.

Two-dimensional material-based functional aerogels for treating hazards in the environment: synthesis, functional tailoring, applications, and sustainability analysis

Environmental pollution is a global problem that endangers human health and ecological balance. As a new type of functional material, two-dimensional material (2DM)-based aerogel is one of the most promising candidates for pollutant detection and environmental remediation. The porous, network-like, interconnected three-dimensional (3D) structure of 2DM-based aerogels can not only preserve the characteristics of the original 2DMs, but also bring many distinct physical and chemical properties to offer abundant active sites for adsorbing and combining pollutants, thereby facilitating highly efficient monitoring and treatment of hazardous pollutants. In this review, the synthesis methods of 2DM aerogels and their broad environmental applications, including various sensors, adsorbents, and photocatalysts for the detection and treatment of pollutants, are summarized and discussed. In addition, the sustainability of 2DM aerogels compared to other water purification materials, such as activated carbon, 2DMs, and other aerogels are analyzed by the Sustainability Footprint method. According to the characteristics of different 2DMs, special focuses and perspectives are given on the adsorption properties of graphene, MXene, and boron nitride aerogels, as well as the sensing and photocatalytic properties of transition metal dichalcogenide/oxide and carbon nitride aerogels. This comprehensive work introduces the synthesis, modification, and functional tailoring strategies of different 2DM aerogels, as well as their unique characteristics of adsorption, photocatalysis, and recovery, which will be useful for the readers in various fields of materials science, nanotechnology, environmental science, bioanalysis, and others.

Near-Infrared Upconversion Mesoporous Tin Dioxide Theranostic Nanocapsules for Synergetic Cancer Chemophototherapy

Smart nanotheranostic systems (SNSs) have attracted extensive attention in antitumor therapy. Nevertheless, constructing SNSs with disease diagnosis ability, improved drug delivery efficiency, inherent imaging performance, and high treatment efficiency remains a scientific challenge. Herein, ultrasmall tin dioxide (SnO₂) was assembled with upconversion nanoparticles (UCNPs) to form mesoporous nanocapsules by an in situ hydrothermal deposition method, followed by loading with doxorubicin (DOX) and modification with bovine serum albumin (BSA). pH/near-infrared dual-responsive nanotheranostics was constructed for computed tomography (CT) and magnetic resonance (MR) imaging-induced collaborative cancer treatment. The mesoporous channel of SnO₂ was utilized as a reservoir to encapsulate DOX, an antineoplastic drug, for chemotherapy and as a semiconductor photosensitizer for photodynamic therapy (PDT). Furthermore, the DOX-loaded UCNPs@SnO₂-BSA nanocapsules combined PDT, Nd³⁺-doped UCNP-triggered hyperthermia effect, and DOX-triggered chemotherapy simultaneously and demonstrated prominently enhanced treatment efficiency compared to the monotherapy model. Moreover, tin, as one of the trace elements in the human body, has a similar X-ray attenuation coefficient to iodine and therefore can act as a contrast agent for CT imaging to monitor the treatment process. Such an orchestrated synergistic anticancer treatment exhibited apparent inhibition of tumor growth in tumor-bearing mice with negligible side effects. Our study demonstrates nanocapsules with excellent biocompatibility and great potential for cancer treatment.

The Effect of rGO-Doping on the Performance of SnO2/rGO Flexible Humidity Sensor

The development of a flexible and high-performance humidity sensor is essential to expand its new applications, such as personal health monitoring and early diagnosis. In this work, SnO₂/rGO nanocomposites were prepared by one-step hydrothermal method. The effect of rGO-doping on humidity sensing performance was investigated. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy were used to characterize the nanostructure, morphology and chemical composition of SnO₂/rGO nanocomposites. The SnO₂/rGO humidity sensitive film was prepared by electrospinning on a polyimide film modified with gold electrodes. The humidity test results show that different doping ratios of rGO have different effects on humidity sensing properties. Among them, the sensor with 2 wt% rGO-doping has a high sensitivity (37,491.2%) within the humidity range as well as the fast response time (80 s) and recover time (4 s). Furthermore, the sensor with 2 wt% rGO-doping remains good flexibility and stability in the case of bending (1000 times). The sensitivity of the 2 wt% rGO-doping sensor at the bending radius (8 mm and 4 mm) is 48,219% and 91,898%, respectively. More importantly, the sensor could reflect different breathing states clearly and track breathing intervals as short as 3 s. The SnO₂/rGO flexible humidity sensor with accuracy, flexibility and instantaneity as well as the facile fabrication strategy is conceivable to be applied in the potential application for human health real-time monitoring.

High Performance Acoustic Wave Nitrogen Dioxide Sensor with Ultraviolet Activated 3D Porous Architecture of Ag-Decorated Reduced Graphene Oxide and Polypyrrole Aerogel

Surface acoustic wave (SAW) devices have been widely explored for real-time monitoring of toxic and irritant chemical gases such as nitrogen oxide (NO₂), but they often have issues such as a complicated process of the sensing layer, low sensitivity, long response time, irreversibility, and/or requirement of high temperatures to enhance sensitivity. Herein, we report a sensing material design for room-temperature NO₂ detection based on a 3D porous architecture of Ag-decorated reduced graphene oxide-polypyrrole hybrid aerogels (rGO-PPy/Ag) and apply UV activation as an effective strategy to further enhance the NO₂ sensing performance. The rGO-PPy/Ag-based SAW sensor with the UV activation exhibits high sensitivity (127.68 Hz/ppm), fast response/recovery time (36.7 s/58.5 s), excellent reproducibility and selectivity, and fast recoverability. Its enhancement mechanisms for highly sensitive and selective detection of NO₂ are based on a 3D porous architecture, Ag-decorated rGO-PPy, p-p heterojunction in rGO-PPy/Ag, and UV photogenerated carriers generated in the sensing layer. The scientific findings of this work will provide the guidance for future exploration of next-generation acoustic-wave-based gas sensors.

Nitrogen Dioxide Gas Sensor Based on Ag-Doped Graphene: A First-Principle Study

High-performance tracking trace amounts of NO2 with gas sensors could be helpful in protecting human health since high levels of NO2 may increase the risk of developing acute exacerbation of chronic obstructive pulmonary disease. Among various gas sensors, Graphene-based sensors have attracted broad attention due to their sensitivity, particularly with the addition of noble metals (e.g., Ag). Nevertheless, the internal mechanism of improving the gas sensing behavior through doping Ag is still unclear. Herein, the impact of Ag doping on the sensing properties of Graphene-based sensors is systematically analyzed via first principles. Based on the density-functional theory (DFT), the adsorption behavior of specific gases (NO2, NH3, H2O, CO2, CH4, and C2H6) on Ag-doped Graphene (Ag–Gr) is calculated and compared. It is found that NO2 shows the strongest interaction and largest Mulliken charge transfer to Ag–Gr among these studied gases, which may directly result in the highest sensitivity toward NO2 for the Ag–Gr-based gas sensor.

Humidity-Insensitive NO2 Sensors Based on SnO2/rGO Composites

This study reported a novel humidity-insensitive nitrogen dioxide (NO₂) gas sensor based on tin dioxide (SnO₂)/reduced graphene oxide (rGO) composites through the sol-gel method. The sensor demonstrated ppb-level NO₂ detection in p-type sensing behaviors (13.6% response to 750 ppb). Because of the synergistic effect on SnO₂/rGO p-n heterojunction, the sensing performance was greatly enhanced compared to that of bare rGO. The limit of detection of sensors was as low as 6.7 ppb under dry air. Moreover, benefited from the formed superhydrophobic structure of the SnO₂/rGO composites (contact angle: 149.0°), the humidity showed a negligible influence on the dynamic response (S_g) of the sensor to different concentration of NO₂ when increasing the relative humidity (RH) from 0 to 70% at 116°C. The relative conductivity of the sensor to 83% relative humidity was 0.11%. In addition, the response ratio (S_g/S_RH) between 750 ppb NO₂ and 83% RH was 649.0, indicating the negligible impaction of high-level ambient humidity on the sensor. The as-fabricated humidity-insensitive gas sensor can promise NO₂ detection in real-world applications such as safety alarm, chemical engineering, and so on.

Recent Progress of Toxic Gas Sensors Based on 3D Graphene Frameworks

Air pollution is becoming an increasingly important global issue. Toxic gases such as ammonia, nitrogen dioxide, and volatile organic compounds (VOCs) like phenol are very common air pollutants. To date, various sensing methods have been proposed to detect these toxic gases. Researchers are trying their best to build sensors with the lowest detection limit, the highest sensitivity, and the best selectivity. As a 2D material, graphene is very sensitive to many gases and so can be used for gas sensors. Recent studies have shown that graphene with a 3D structure can increase the gas sensitivity of the sensors. The limit of detection (LOD) of the sensors can be upgraded from ppm level to several ppb level. In this review, the recent progress of the gas sensors based on 3D graphene frameworks in the detection of harmful gases is summarized and discussed.

Pd-Doping-Induced Oxygen Vacancies in One-Dimensional Tungsten Oxide Nanowires for Enhanced Acetone Gas Sensing

Metal oxide semiconductors (MOS) with different nanostructures have been widely used as gas sensing materials due to the tunable interface structures and properties. However, further improvement of the sensing sensitivity and selectivity is still challenging in this area. Constructing appropriate heterogeneous interface structures and oxygen vacancies is one of the important strategies to tune the sensing properties of MOS. In the present study, interfacial heterostructures in Pd_xW₁₈O₄₉ nanowires (Pd_xW₁₈O₄₉ NWs) were fabricated and manipulated by doping different Pd contents through a simple hydrothermal process. Relevant characterization proved that the structure and composition of the one-dimensional (1D) nanomaterial can be effectively changed by Pd doping. It was found that the oxygen vacancy concentration increases first with the increase of Pd content, and when the Pd content increases to 7.18% (Pd_7.18%W₁₈O₄₉ NWs), the oxygen vacancy content reaches the maximum (52.5%). If the Pd content continues to increase, the oxygen vacancy ratio decreases. The gas sensing investigations illustrated that the Pd_xW₁₈O₄₉ NWs exhibited enhanced sensing properties than pure W₁₈O₄₉ NWs toward acetone. Among the as-prepared catalysts, the Pd_7.18%W₁₈O₄₉ NWs showed the best sensing response and the fastest response-recovery speeds (5 and 10 s, respectively) at a working temperature of 175 °C. In addition, this 1D nanostructure with fabricated heterostructures also delivers a good sensing selectivity and a wide detection range from 100 ppb to 300 ppm, with maintaining excellent performance in the presence of high concentrations of ethanol and carbon dioxide. The excellent gas sensing behavior could be attributed to the generated oxygen vacancies and the heterostructures upon Pd doping. This study offers a novel strategy for the design of high-performance gas sensors for ppb-level acetone sensing.

Chemical Surface Adsorption and Trace Detection of Alcohol Gas in Graphene Oxide-Based Acid-Etched SnO2 Aerogels

An acidified SnO₂/rGO aerogel (ASGA) is an attractive contributor in ethanol gas sensing under ultralow concentration because of the sufficient active sites and adsorption pores in SnO₂ and the rGA, respectively. Furthermore, a p-n heterojunction is successfully constructed by the high electron mobility between ASP and rGA to establish a brand-new bandgap of 2.72 eV, where more electrons are released and the surface energy is decreased, to improve the gas sensitivity. The ASGA owns a specific surface area of 256.1 m²/g, far higher than SnO₂ powder (68.7 m²/g), indicating an excellent adsorption performance, so it can acquire more ethanol gas for a redox reaction. For gas-sensing ability, the ASGA exhibits an excellent response of R_a/R_g = 137.4 to 20 ppm of ethanol at the optimum temperature of 210 °C and can reach a response of 1.2 even at the limit detection concentration of 0.25 ppm. After the concentration gradient change test, a nonlinear increase between concentration and sensitivity (S-C curve) is observed, and it indirectly proves the chemical adsorption between ethanol and ASGA, which exhibits charge transfer and improves electron mobility. In addition, a detailed energy band diagram and sensor response diagram jointly depict the gas-sensitive mechanism. Finally, a conversed calculation explains the feasibility of the nonlinear S-C curve from the atomic level, which further verifies the chemical adsorption during the sensing process.

The mechanical property and microscopic deformation mechanism of nanoparticle-contained graphene foam materials under uniaxial compression

Nanoparticle-contained graphene foams have found more and more practical applications in recent years, which desperately requires a deep understanding on basic mechanics of this hybrid material. In this paper, the microscopic deformation mechanism and mechanical properties of such a hybrid material under uniaxial compression, that are inevitably encountered in applications and further affect its functions, are systematically studied by the coarse-grained molecular dynamics simulation method. Two major factors of the size and volume fraction of nanoparticles are considered. It is found that the constitutive relation of nanoparticle filled graphene foam materials consists of three parts: the elastic deformation stage, deformation with inner re-organization and the final compaction stage, which is much similar to the experimental measurement of pristine graphene foam materials. Interestingly, both the initial and intermediate modulus of such a hybrid material is significantly affected by the size and volume fraction of nanoparticles, due to their influences on the microstructural evolution. The experimentally observed 'spacer effect' of such a hybrid material is well re-produced and further found to be particle-size sensitive. With the increase of nanoparticle size, the micro deformation mechanism will change from nanoparticles trapped in the graphene sheet, slipping on the graphene sheet, to aggregation outside the graphene sheet. Beyond a critical relative particle size 0.26, the graphene-sheet-dominated deformation mode changes to be a nanoparticle-dominated one. The final microstructure after compression of the hybrid system converges to two stable configurations of the 'sandwiched' and 'randomly-stacked' one. The results should be helpful not only to understand the micro mechanism of such a hybrid material in different applications, but also to the design of advanced composites and devices based on porous materials mixed with particles.

Understanding the Joule-heating behaviours of electrically-heatable carbon-nanotube aerogels

Cylindrical monolithic, electrically-heatable reduced carbon nanotube (rCNT) aerogels were synthesized to exploit their Joule-heating behaviours using two different arrangements (i.e. the top-bottom arrangement and the side-side arrangement) under different compressive strains. The top-bottom arrangement results in faster heating kinetics (up to 286 K min^-1), higher heating efficiency (up to 80 °C W^-1), a more uniform temperature distribution profile and higher electro-thermal conversion efficiency than the side-side arrangement. This study provides fundamental perspectives for exploiting the Joule-heating behaviours of geometrically complex nanocarbon aerogels, and thus will have important implications in strain-sensitive materials.

Fully Inkjet-Printed Mesoporous SnO2-Based Ultrasensitive Gas Sensors for Trace Amount NO2 Detection

Printed sensors are among the most successful groups of devices within the domain of printed electronics, both in terms of their application versatility and the emerging market share. However, reports on fully printed gas sensors are rare in the literature, even though it can be an important development toward fully printed multisensor platforms for diagnostics, process control, and environmental safety-related applications. In this regard, here, we present the traditional tin oxide-based completely inkjet-printed co-continuous and mesoporous thin films with an extremely large surface-to-volume ratio and then investigate their NO₂ sensing properties at low temperatures. A method known as evaporation-induced self-assembly (EISA) has been mimicked in this study using pluronic F127 (PEO₁₀₆-PPO₇₀-PEO₁₀₆) as the soft templating agent and xylene as the micelle expander to obtain highly reproducible and spatially homogeneous co-continuous mesoporous crystalline SnO₂ with an average pore diameter of the order of 15-20 nm. The fully printed SnO₂ gas sensors thus produced show high linearity for NO₂ detection, along with extremely high average response of 11,507 at 5 ppm NO₂. On the other hand, the sensors show an ultralow detection limit of the order of 20 ppb with an easy to amplify response of 31. While the excellent electronic transport properties along such co-continuous, mesoporous structures are ensured by their well-connected (co-continuous) ligaments and pores (thereby ensuring high surface area and high mobility transport at the same time) and may actually be responsible for the outstanding sensor performance that has been observed, the use of an industrial printing technique ascertains the possibility of high-throughput manufacturing of such sensor units toward inexpensive and wide-range applications.

Hydrogenation-produced In2O3/InN core-shell nanorod and its effect on NO2 gas sensing behavior

In this work, for the first time, we have made InN/In₂O₃ core-shell heterostructure by hydrogen plasma treatment. InN nanorods (NRs) were grown by using plasma-assisted molecular beam epitaxy, and hydrogen plasma treatment was performed by using reactive ion etching at room temperature. From x-ray photoemission spectroscopy studies, it was observed that the bonding partner of In changes from N to O and N 1s completely disappeared in the hydrogenated InN NRs. Furthermore, high-resolution transmission electron microscopy revealed the formation of InN/In₂O₃ core-shell NRs by hydrogenation plasma treatment. The resistance of pristine InN NRs was decreased in NO₂ ambient. Interestingly, the resistance of the InN/In₂O₃ core-shell was increased while introducing NO₂ gas. InN NR surface exhibits downward band bending due to the electron accumulation, in NO₂ ambient, and the surface band bending was decreased due to the increase in the bulk conduction channel. This reversed gas sensing behavior in InN/In₂O₃ core-shell NRs was attributed to the increase in depletion layer while reducing the conduction channel width by the absorption of NO₂. The InN/In₂O₃ coreshell NRs exhibited a response of 22.43% at 50 °C, which was 5.11 times higher than that of pristine InN NRs.

Ag-Modified 3D Reduced Graphene Oxide Aerogel-Based Sensor with an Embedded Microheater for a Fast Response and High-Sensitive Detection of NO2

A chemiresistive gas sensor based on a three-dimensional Ag-modified reduced graphene oxide (3D Ag-rGO) aerogel is reported. We improve the graphene-based sensor performance by optimization of operating temperature, chemical modification, and new design of the material geometrical structure. The self-assembly and Ag nanoparticle (NP) decoration of the Ag-rGO aerogel are realized by a facile, one-step hydrothermal method. An integrated low-power microheater fabricated on a micromachined SiO₂ membrane is employed to enhance the performance of the sensor with a fast response to NO₂ and a shortened recovery time. The 3D Ag-rGO-based sensor at a temperature of 133 °C exhibits the highest response. At the same time, the response to other gases is suppressed while the response of the Ag-rGO sensor toward ammonia at 133 °C is reduced to half of the value at room temperature, demonstrating a greatly improved selectivity toward NO₂. Additionally, the sensor exhibits a remarkably fast response to 50 ppb NO₂ and a low limit of detection of 6.9 ppb.

Alveolus-Inspired Active Membrane Sensors for Self-Powered Wearable Chemical Sensing and Breath Analysis

Fossil fuel internal combustion engines generate and release a huge amount of nitrogen dioxide, leading to respiratory and allergic diseases such as asthma, pneumonia, and possibly tuberculosis. Here we develop an alveolus-inspired membrane sensor (AIMS) for self-powered wearable nitrogen dioxide detection and personal physiological assessment. The bionic AIMS exhibits an excellent sensitivity up to 452.44%, a good linearity of 0.976, and superior selectivity under a NO₂ concentration of 50 ppm. Furthermore, the AIMS can also be employed to diagnose human breath behaviors for breath analysis. The fundamental sensing mechanism is established using a combination of thermodynamic analysis, finite-element analysis, and phase-field simulations. It is found that the depolarization field inside the sensitive materials plays a crucial role in the self-powered gas-sensing performance. This work not only provides an efficient, low-cost, portable, and environmentally friendly means for active environmental assessment and personal biomonitoring but also provides a deep understanding of the gas-sensing mechanisms.

Green Synthesis of 3D Chemically Functionalized Graphene Hydrogel for High-Performance NH3 and NO2 Detection at Room Temperature

To address the low gas sensitivity of pristine graphene (Gr), chemical modification of Gr has been proved as a promising route. However, the existing chemical functionalization method imposes the utilization of toxic chemicals, increasing the safety risk. Herein, vitamin C (VC)-modified reduced graphene hydrogel (V-RGOH) is synthesized via a green and facile self-assembly process with the assistance of biocompatible VC molecules for high-performance NH₃ and NO₂ detection. The three-dimensional (3D) structured V-RGOH is highly sensitive to low-concentration NH₃ and NO₂ at room temperature. In comparison with those of the unmodified RGOH, the V-RGOH gas sensors display an order of magnitude higher sensitivity and much lower limit of detection, resulting from the enhanced interaction between VC and analytes. NH₃ and NO₂ with extremely low concentrations of 500 and 100 ppb are detected experimentally. Notably, imbedded microheaters are exploited to explore the temperature-dependent gas sensing properties, revealing the negative and positive impacts of temperature on the sensitivity and recovery speed, respectively. Notably, the V-RGOH sensor exhibits remarkable selectivity and linearity and a wide detection range. This work reveals the remarkable effects of chemical modification with biodegradable molecules and 3D structure design on improving the gas sensing performance of the Gr material.

Observation of Switchable Dual-Conductive Channels and Related Nitric Oxide Gas-Sensing Properties in the N-rGO/ZnO Heterogeneous Structure

Gas sensors based on hybrid materials of graphene oxide/metal oxide semiconductors are an effective way to improve sensor performance. In this paper, we demonstrate a high-performance nitric oxide (NO) gas sensor based on nitrogen-doped reduced graphene oxide/ZnO nanocrystals (N-rGO/ZnO) operating at a low work temperature. ZnO nanocrystals, with an average size of approximately 5 nm, can be uniformly and compactly anchored on the surface of N-rGO using a facile two-step hydrothermal synthesis with an appropriate amount of ammonia as the nitrogen source. The sensor based on the N-rGO/ZnO composite with 0.3 mL of ammonia (N-rGO/ZnO-0.3), in comparison with N-rGO/ZnO with different amounts of ammonia, N-rGO, and rGO/ZnO, exhibited a significantly higher sensitivity (S = R_g/R_a) at the parts per billion (ppb) level for NO gas at 90 °C. The maximum sensitivity at 800 ppb NO was approximately 22, with much faster response and recovery times. In addition, the N-rGO/ZnO-0.3 sensor revealed great stability, a low detection limit of 100 ppb, and an excellent selectivity toward NO versus other gases (NO₂, H₂, CO, NH₃, and CH₄), especially at the ppb level. More interestingly, when exposed to oxidizing and reducing gases, unlike conventional semiconductor sensitive materials with resistances that normally change in the opposite direction, only the increase in the resistance is surprisingly and incomprehensibly observed for the N-rGO/ZnO-0.3 sensor. The peculiar sensing behaviors cannot be explained by the conventional theory of the adsorption process, redox reactions on the surfaces, and the well-defined p-n junction between N-rGO and ZnO, originating from the chemical bonding of Zn-C. We propose here for the first time that switchable contribution from dual-conduction paths including the corresponding ZnO channel with the p-n junction and the corresponding N-rGO channel to the sensitivity may exist in the interaction between gases and N-rGO/ZnO-0.3 material. When an oxidizing gas (such as NO) is exposed to the N-rGO/ZnO-0.3 sensor, the contribution from the conductive channel of ZnO nanoparticles and the p-n junction to the sensitivity is dominant. On the contrary, as for a reducing gas (such as H₂), the contribution alters to the N-rGO channel as the dominating mode for sensitivity. For gas-sensing behavior of the NGZ-0.1 and NGZ-0.5 sensors, there is only one conduction path from the N-rGO channel for the sensitivity. The model of switchable dual-conduction paths has addressed the mysterious response observed for different gases, which may be utilized to enlighten the understanding of other application problems in nanoscale hybrid materials with a heterogeneous structure.

Graphene-Based Thermoacoustic Sound Source

Thermoacoustic (TA) effect has been discovered for more than 130 years. However, limited by the material characteristics, the performance of a TA sound source could not be compared with magnetoelectric and piezoelectric loudspeakers. Recently, graphene, a two-dimensional material with the lowest heat capacity per unit area, was discovered to have a good TA performance. Compared with a traditional sound source, graphene TA sound sources (GTASSs) have many advantages, such as small volume, no diaphragm vibration, wide frequency range, high transparency, good flexibility, and high sound pressure level (SPL). Therefore, graphene has a great potential as a next-generation sound source. Photoacoustic (PA) imaging can also be applied to the diagnosis and treatment of diseases using the photothermo-acoustic (PTA) effect. Therefore, in this review, we will introduce the history of TA devices. Then, the theory and simulation model of TA will be analyzed in detail. After that, we will talk about the graphene synthesis method. To improve the performance of GTASSs, many strategies such as lowering the thickness and using porous or suspended structures will be introduced. With a good PTA effect and large specific area, graphene PA imaging and drug delivery is a promising prospect in cancer treatment. Finally, the challenges and prospects of GTASSs will be discussed.

Laser Writing of Janus Graphene/Kevlar Textile for Intelligent Protective Clothing

Protective clothing plays a vital role in safety and security. Traditional protective clothing can protect the human body from physical injury. It is highly desirable to integrate modern wearable electronics into a traditional protection suit to endow it with versatile smart functions. However, it is still challenging to integrate electronics into clothing through a practical approach while keeping the intrinsic flexibility and breathability of textiles. In this work, we realized the direct writing of laser-induced graphene (LIG) on a Kevlar textile in air and demonstrated the applications of the as-prepared Janus graphene/Kevlar textile in intelligent protective clothing. The C═O and N-C bonds in Kevlar were broken, and the remaining carbon atoms were reorganized into graphene, which can be ascribed to a photothermal effect induced by the laser irradiation. Proof-of-concept devices based on the prepared graphene/Kevlar textile, including flexible Zn-air batteries, electrocardiogram electrodes, and NO₂ sensors, were demonstrated. Further, we fabricated self-powered and intelligent protective clothing based on the graphene/Kevlar textile. The laser-induced direct writing of graphene from commercial textiles in air conditions provides a versatile and rapid route for the fabrication of textile electronics.

Multifunctional Inorganic Nanomaterial Aerogel Assembled into fSWNT Hydrogel Platform for Ultraselective NO2 Sensing

Facile fabrication of multifunctional porous inorganic aerogels remains an outstanding challenge despite the considerable demand for extensive applications. Here, we present the production of a multifunctional porous inorganic nanomaterial aerogel by controllable surface chemistry of a functionalized SWNT (fSWNT) hydrogel platform for the first time. The versatile functional inorganic nanoparticles can be incorporated uniformly on the porous 3D fSWNT hydrogel platform through a facile dip coating method at ambient conditions. The morphology of the multifunctional inorganic aerogel is manipulated by designing the fSWNT hydrogel platform for different requirements of applications. In particular, Pt-SnO₂@fSWNT aerogels exhibit high porosity and uniformly distributed ultrafine Pt and SnO₂ on the fSWNT platform with controllable particle size (1.5-3.5 nm), which result in significantly high surface area (393 m² g^-1). The ultrafine Pt-SnO₂@fSWNT aerogels exhibit highly sensitive (14.77% at 5 ppm) and selective NO₂ sensing performance even at room temperature due to the increased active surface area and controllable porous structure of the ultrafine aerogel, which can provide fast transport and penetration of a target gas into the sensing layers. The newly designed multifunctional inorganic aerogel with ultrahigh surface area and high open porosity is a prospective materials platform of high performance gas sensors, which could be also broadly expanded to widespread applications including catalysis and energy storages.

Recent advances in amphiphilic block copolymer templated mesoporous metal-based materials: assembly engineering and applications

Mesoporous metal-based materials (MMBMs) have received unprecedented attention in catalysis, sensing, and energy storage and conversion owing to their unique electronic structures, uniform mesopore size and high specific surface area. In the last decade, great progress has been made in the design and application of MMBMs; in particular, many novel assembly engineering methods and strategies based on amphiphilic block copolymers as structure-directing agents have also been developed for the "bottom-up" construction of a variety of MMBMs. Development of MMBMs is therefore of significant importance from both academic and practical points of view. In this review, we provide a systematic elaboration of the molecular assembly methods and strategies for MMBMs, such as tuning the driving force between amphiphilic block copolymers and various precursors (i.e., metal salts, nanoparticles/clusters and polyoxometalates) for pore characteristics and physicochemical properties. The structure-performance relationship of MMBMs (e.g., pore size, surface area, crystallinity and crystal structure) based on various spectroscopy analysis techniques and density functional theory (DFT) calculation is discussed and the influence of the surface/interfacial properties of MMBMs (e.g., active surfaces, heterojunctions, binding sites and acid-base properties) in various applications is also included. The prospect of accurately designing functional mesoporous materials and future research directions in the field of MMBMs is pointed out in this review, and it will open a new avenue for the inorganic-organic assembly in various fields.

3D synergistical rGO/Eu(TPyP)(Pc) hybrid aerogel for high-performance NO2 gas sensor with enhanced immunity to humidity

The prevalence of Internet of Things and portable electronics create an unprecedented demand for the high performance gas sensors. To pursuit such sensor, sandwich-type (phthalocyaninato)(porphyrinato) europium double-decker complex Eu(TPyP)(Pc) [TPyP = meso-tetra(4-pyridyl)porphyrin; Pc = phthalocyanine] was in situ self-assembled on the surface of reduced graphene oxide (rGO) driven by the π-π interaction, forming a 3D synergistical rGO/Eu(TPyP)(Pc) hybrid aerogel. The resulting aerogel not only effectively integrates the gas sensing of Eu(TPyP)(Pc) and good conductivity of rGO, but also exhibited a prominent synergy effect. Ascribed to the attractive properties, the fabricated NO₂ gas sensor exhibits superior sensitivity and selectivity in the range of 0.5 to 100 ppm with an extremely low theoretical limit level of detection (80 ppb) at ambient temperature. The response and recovery time of rGO/Eu(TPyP)(Pc) hybrid aerogel based sensor to20 ppm NO₂ were 172 and 828 s, respectively. Remarkably, the hydrophobic porous structure of rGO/Eu(TPyP)(Pc) hybrid aerogel endows the prepared sensor with excellent immunity to high relative humidity, which conquered the key technical issue of real application. The present sensor, simultaneously featured with high performance, low-power consumption, and good tolerance to environmental variations, is anticipated to offer the "on-site" and "on-line" measurement tool in real samples.

Stability and Sensing Enhancement by Nanocubic CeO2 with {100} Polar Facets on Graphene for NO2 at Room Temperature

Metal oxides with a polar surface interact strongly with polar NO₂ molecules, thus facilitating sensitive detection of NO₂. In this work, the composites comprising graphene and cubic CeO₂ nanoparticles with the {100} polar surface are prepared by a hydrothermal technique, and they exhibit fast response, excellent selectivity, stable recovery, and sensitive detection with a low detection limitation of 1 ppm for NO₂ at room temperature. According to the first-principle calculations, the adsorption energy of NO₂ on the CeO₂{100} polar surface is the most negative corresponding to the strongest interactions between them. The formation energy of oxygen vacancies (O_v) on the {100} polar plane is also negative, and the abundant O_v facilitates the adsorption of NO₂. The internal electric field near the polar surface promotes the charge separation and accelerates the charge exchange between NO₂ and the composites. In addition, graphene promotes electron transfer at the interface and improves the stability of the CeO₂{100} polar surface. The composites of graphene and metal oxides with a polar surface are excellent for NO₂ detection, and the discovery reveals a new sensing strategy.

Three-Dimensional Graphene Hydrogel Decorated with SnO2 for High-Performance NO2 Sensing with Enhanced Immunity to Humidity

A facile, one-step hydrothermal route was exploited to prepare SnO₂-decorated reduced graphene oxide hydrogel (SnO₂/RGOH) with three-dimensional (3D) porous structures for NO₂ gas detection. Various material characterizations demonstrate the effective deoxygenation of graphene oxide and in situ growth of rutile SnO₂ nanoparticles (NPs) on 3D RGOH. Compared with the pristine RGOH, the SnO₂/RGOH displayed much lower limit of detection (LOD) and an order of magnitude higher sensitivity, revealing the distinct impact of SnO₂ NPs in improving the NO₂-sensing properties. An exceptional low theoretical LOD of 2.8 ppb was obtained at room temperature. The p-n heterojunction formed at the interface between RGOH and SnO₂ facilitates the charge transfer, improving both the sensitivity in NO₂ detection and the conductivity of hybrid material. Considering that existing SnO₂/RGO-based NO₂ sensors suffer from great vulnerability to humidity, here we employed integrated microheaters to effectively suppress the response to humidity, with nearly unimpaired response to NO₂, which boosted the selectivity. Notably, a flexible NO₂ sensor was constructed on a liquid crystal polymer substrate with endurance to mechanical deformation. This work indicates the feasibility of optimizing the gas-sensing performance of sensors by combining rational material hybridization, 3D structural engineering with temperature modulation.

On-chip assembly of 3D graphene-based aerogels for chemiresistive gas sensing

Integration of the material preparation step into the device fabrication process is of prime importance for the development of high performance devices. This study presents an innovative strategy for the in situ assembly of graphene-based aerogels on a chip by polymerization-reduction and annealing processes, which are applied as chemiresistive gas sensors for the detection of NO2.

Gas-Sensing Activity of Amorphous Copper Oxide Porous Nanosheets

In this paper, the gas-sensing properties of copper oxide porous nanosheets in amorphous and highly crystalline states were comparatively investigated on the premise of almost the same specific surface area, morphology and size. Unexpectedly, the results show that amorphous copper oxide porous nanosheets have much better gas sensing properties than highly crystalline copper oxide to a serious of volatile organic compounds, and the lowest detection limit (LOD) of the amorphous copper oxide porous nanosheets to methanal is even up to 10 ppb. By contrast, the LOD of the highly crystalline copper oxide porous nanosheets to methanal is 95 ppb. Experiments prove that the oxygen vacancies contained in the amorphous copper oxide porous nanosheets play a key role in improving gas sensitivity, which greatly improve the chemical activity of the materials, especially for the adsorption of molecules containing oxygen-groups such as methanal and oxygen.

Graphene aerogel nanoparticles for in-situ loading/pH sensitive releasing anticancer drugs

Free polymer graphene aerogel nanoparticles (GA NPs) were synthesized by using reduction/aggregation of graphene oxide (GO) sheets in the presence of vitamin C (as a biocompatible reductant agent) at a low temperature (40 °C), followed by an effective sonication. Synthesis of GA NPs in doxorubicin hydrochloride (DOX)-containing solution results in the simultaneous synthesis and drug loading with higher performance (than that of the separately synthesized and loaded samples). To investigate the mechanism of loading and the capability of GA NPs in the loading of other drug structures, two groups of ionized (DOX, Amikacin sulfate and, d-glucosamine hydrochloride) and non-ionized (Paclitaxel (PTX)) drugs were examined. Furthermore, the relationship between the bipolar level of DOX solution (contributing to H-bonding of DOX and GO) and the amount of DOX loading was investigated. The DOX showed higher loading (>3 times) than PTX, as anticancer drugs. Since both DOX and PTX possess aromatic structures, the higher loading of DOX was assigned to its positive partial charge and ionized nature. Accordingly, other drugs (having positive partial charge and ionized nature, but no aromatic structure) such as Amikacin sulfate and d-glucosamine hydrochloride presented higher loading than PTX. These results indicated that although the π-π interactions induced by aromatic structures are important in drug loading, the electrostatic interaction of ionized drugs with GO (especially through H-bonding) is the dominant mechanism. DOX-loaded GANPs showed high pH-sensitive release (equivalent to the carrier weight) after 5 days, which can indicate benefits in tumor cell acidic microenvironments in-vivo.