Implementing sensitive and fast ppb-level formaldehyde sensing at room temperature is still in extreme demand for practical indoor air quality monitoring. Herein, we developed a visible-light-sensitive and dipole-modified graphene-based nanocomposite ZnO_x@ANS-rGO for ultrasensitive trace formaldehyde sensing. The rich oxygen vacancy zinc oxide (ZnO_x) nanoparticles on graphene nanosheets provide OH-groups and edge sorption sites to facilitate the activation of adsorbed oxygen. Moreover, the supramolecular assembled 5-aminonaphthalene-1-sulfonic acid-modified graphene (ANS-rGO) nanosheets with donor–π–acceptor dipole served as an excellent conduction platform to transport and collect photo-generated electrons. Based on the collaboration of rich ZnO_x and ANS-rGO, the obtained sensor ZnO_x@ANS-rGO-0.1 showed the highest response (R_a/R_g = 1.58 to 1 ppm HCHO) among the MOS materials reported so far, and its limit of detection (LOD) can be as low as 5 ppb under 405 nm light illumination at RT. The outstanding efficiency and accuracy of the obtained gas sensor were confirmed by practical performance estimation in a 30 m³ chamber. The selectivity, long-term stability, repeatability and humidity resistance of the obtained sensors at RT were also revealed. The sensing mechanism based on the combination of visible-light activation and dipole modification was analyzed by the O-XPS, PL, in situ ATR-FTIR and charge density difference calculation.

A flexible high-performance room temperature NH₃ sensor was fabricated using a PSS-rGO/PANI network, which was synthesized via supramolecular assembly, controlled freeze-drying technology, and a facile interfacial polymerization route.

Gas sensing materials essentially dominate the performances of the gas sensors which are widely applied in environmental monitoring, industrial production and medical diagnosis. However, most of the traditional gas sensing materials show excellent performances only at high operating temperatures, which are high energy consumptive and have potential issues in terms of reliability and safety of the sensors. Therefore, the development of Room Temperature (RT) gas sensing materials becomes a research hotspot in this field. In recent years, graphene-based materials have been studied as a class of promising RT gas sensing materials because graphene has a unique twodimensional (2D) structure with high electron mobility and superior feasibility of assembling with other “guest components” (mainly small organic molecules, macromolecules and nanoparticles). More interestingly, its electrical properties become even more sensitive toward gas molecules at RT after surface modification. In this review, we have summarized the recently reported graphenebased RT gas sensing materials for the detection of NO2, H2S, NH3, CO2, CO, SO2, Volatile Organic Compounds (VOCs) (i.e. formaldehyde, acetone, toluene, ethanol), as well as Liquefied Petroleum Gas (LPG) and highlighted the latest researches with respect to supramolecular modification of graphene for gas sensing. The corresponding structural features and gas sensing mechanisms of the graphene-based gas sensors have also been generalized.

The measurement of humidity is of great significance for precision instruments, semiconductor integrated circuits, and element manufacturing factories. The oxygen-containing groups and noble metals in graphene-based sensing materials can significantly influence their humidity-sensing performance. Herein, 1,3,5-benzenetricarboxylic acid-functionalized reduced graphene oxide (H3BTC-rGO) loaded with Ag nanocluster nanocomposites (H3BTC-rGO/Ag) was synthesized via a facile one-step reduction method. The H3BTC-rGO/Ag-based sensor exhibited excellent humidity-sensing performance, including a higher sensitivity of 88.9% and a faster response/recovery time of 9 s/16 s towards 50% RH than those of other GO-, rGO-, and H3BTC-rGO-based sensors. The proposed humidity sensor was tested in the range of 0% to 100% RH and showed excellent sensitivity even at a low relative humidity of 0–10% or a high relative humidity of 90–100%. In addition, the H3BTC-rGO/Ag-based sensor had excellent selectivity, reliable repeatability, and good stability over 30 days under different relative humidities. Compared with H3BTC-rGO-200, the H3BTC-rGO/Ag-0.25-based sensor exhibited a low hysteresis of less than ±5% RH. The high performance was ascribed to the high density of the carboxyl groups and good conductivity of H3BTC-rGO, as well as the catalytic role of the Ag nanoclusters, resulting in high water adsorption rates. The potential applications of the H3BTC-rGO/Ag-based humidity sensor in human exhalation monitoring are also discussed. This work provides a reference for the application of graphene-based flexible sensors in monitoring very wet and dry environments.

In this work, MXene and Ag nanoparticle (Ag NP)–decorated aligned Ag nanowires (Ag NWs) are applied to achieve surface-enhanced Raman scattering (SERS). MXene/Ag NP–decorated aligned Ag NWs based PDMS (polydimethylsiloxane) (MAAP) substrate is fabricated following the order of oil–water–air interfacial self-assembly of aligned Ag NWs, then surface modification of Ag NPs, and drop-casting of MXene last. The synergistic effect of MXene and Ag NP–decorated Ag NWs confers the MAAP substrate with high sensitivity, universality (limit of detection of 10⁻¹⁰ M for rhodamine 6G and crystal violet, 10⁻⁹ M for malachite green), and reproducibility. Based on the existence of PDMS, the MAAP substrate exhibits a good flexibility, and it maintains a high Raman activity after stretching and bending for 100 times. In addition, the surface covering MXene prevents Ag NWs decorated by Ag NPs from oxidation, which made the MAAP substrate still have a relatively high Raman activity. The fabricated MAAP substrate enriches the family members of MXene-based SERS substrates and displays an application value in SERS on irregular surfaces.