Colloidal luminescent quantum dots doped with metal ions as electronic dopants present significant potential for future optoelectronic devices and spin-based technologies. Metal ions, Cu2+, Mo4+ and Ag+, were doped into the lattice of Bi2Se3 QDs respectively, and the emission color was tuned precisely from yellow to blue green by controlling the molar doping concentration of Cu2+ or Mo4+ ions. The luminescence stability of Bi2Se3 QDs was greatly improved by synthesizing core@shell structure of Bi2Se3: Ag+@Ag2Se QDs. Compared with that for Bi2Se3 QDs, the absolute maximum quantum yields for Bi2Se3: Cu2+ QDs, Bi2Se3: Mo4+ QDs and Bi2Se3: Ag+ QDs were enhanced 21.1%, 15.2% and 43.5% respectively. As for Bi2Se3: Mo4+ QDs, the full width at half maximum was decreased from 125.25 nm to 93.31 nm as the molar concentration of Mo4+ ions was increased from 0% to 20%. The luminescence properties for Bi2Se3 QDs doped with metal ions (Cu2+, Mo4+ and Ag+) were investigated in detail using excitation and emission spectra, lifetime data and quantum yield data. The results might provide new method and ideas for the regulation of the emission color of metal compound quantum dots, and provide new ideas for increasing the luminescence quantum yield and improving the luminescence stability.

The severe impact of humidity on low-temperature sensing performance has long been an urgent issue to be addressed in the field of semiconductor gas sensors. In many scenarios, such as breath analysis, sewers, swamps and mines, H2S coexists with a large amount of water vapor, making it particularly necessary to improve its low-temperature moisture resistance. In this paper, A HEA was fabricated and employed to improve the low-temperature moisture resistance of SnO2-based H2S sensors. The results show that 1.5 wt% HEA modified SnO2 exhibits the best sensitization performance toward H2S gas sensor, and excellent moisture resistance at low temperatures. At high relative humidity (RH = 80%), a response of 15 was maintained with no decline over the 7-day test period. At the same time, it can also enhance the H2S (0.5 ppm) response on SnO2 from 1.2 to 22, lower the response time from 30 s to 4 s, the recovery time from 140 s to 101 s, and decrease the limit of detection (LOD) down to 41 ppb at 70 °C. Theoretical calculations show that HEA can enhance the competitive adsorption of oxygen to water, thereby increasing the concentration of reactive oxygen species (ROS). Additionally, the electron transfer from HEA to SnO2 can jointly regulate the energy-to-structure and carrier concentration of SnO2, promoting the adsorption of oxygen and the reaction with H2S. This study offers a new strategy for improving the low-temperature performance of gas sensors under high-humidity environments.

Enhancing the gas-sensing properties of metal oxide semiconductors using noble metals' electronic and chemical sensitization functions is a common approach to develop high-performance gas sensors. However, the high cost and scarcity of noble metals pose challenges to sustainability. In this study, a non-noble metal MnFeCoNiCu high-entropy alloy (HEA) was designed as an alternative to noble metals to enhance the sensitivity of SnO2 and enable efficient, stable, and rapid detection of acetone (C3H6O). The MnFeCoNiCu HEA-loaded SnO2 demonstrated improved performance in C3H6O detection, including high selectivity (κ > 3), a high sensitivity (Ra/Rg = 4.17 at 0.5 ppm), a low detection limit (30 ppb), fast response and recovery time (4.6 s/5 s), long-term stability (over 50 days), and resistance to humidity (stable at 90% RH). The enhanced performance of the HEA is attributed to the fact that it possesses more valence electrons and the electrons can transfer and redistribute among different atoms, which leads to an increase in active oxygen species and catalytic sites, promoting electron sensitization. This study provides insights into designing and developing a highly catalytic, non-noble metal HEA for gas-sensing applications.

Triethylamine (TEA) is one of the most critical raw materials used in the industry. Due to its toxic and harmful characteristics, it is crucial to develop high-performance gas sensors for detecting TEA rapidly and precisely. This study focuses on enhancing the gas sensing performance of In2O3 by partially replacing In3+ with Al3+. The result proved that the introduction of Al3+ into In2O3 can generate a hollow structure to promote the diffusion of the gas, alter the valence band structure to facilitate the oxidation of TEA, and result in more oxygen vacancies to promote the formation of charge carriers. The combination of these factors leads to the enhanced gas-sensing performance of In2O3. The TEA response value of the 5 mol% Al-In2O3 reached 2.7 times that of pure In2O3 at a relatively low working temperature of 120 degrees C, and the response and recovery time were shortened from 26 s and 147 s to 18 sand 138 s. Moreover, the response values were almost unchanged at high humidity (25 degrees C, 80 % RH) and after 30 days of continuous testing at 120 degrees C. The theoretical detection limit was 31 ppb. This research provides an excellent gas-sensing material for triethylamine detection and a deep understanding of the structure-activity relationship in metal oxide semiconductor materials' gas-sensing mechanisms, thus providing new insights for designing other high-performance gas-sensing materials.

Viologen materials have attracted much attention due to the sensitive stimulus response to color change under appropriate external stimuli, yet the chromic mechanism has rarely been explored in depth. Herein, a novel viologen-based Zn-MOF of {[Zn(Vio)(o-PTA)]·2H2O}n has been synthesized by a newly designed viologen derivative (HVio·Br), phthalic acid (o-H2PTA) and Zn2+ ions, exhibiting a sensitive 5-fold responsive color change (photo-/chemo-/hydro-/thermo-/electrochromism). Due to the introduction of an acetophenone substituent on Vio, it can serve as both an electron acceptor and an electron donor. Therefore, Zn-MOF exhibits a photoinduced blue through intramolecular electron transfer (ET), and NH3 stimulated orange through intermolecular ET. o-PTA2- as another donor can form a new donor-acceptor (D-A) system with Vio, which helps to achieve thermally and electrically induced purple through intermolecular ET. All chromic behaviors are visible to the naked eye and have superior reversibility and cycling stability. The different chromic mechanisms have been first studied in situ by crystal structure and X-ray photoelectron spectroscopy (XPS) results before and after color change. Zn-MOF also displays dynamically adjustable fluorescence intensity by UV exposure time, temperature, and acid-base vapors, making it applicable for high-security information applications. This work provides valuable insight for the rational design of next-generation multiresponsive chromic materials.

Red efficient luminescent carbon quantum dots are still difficult to be synthesized. In this work, red carbon quantum dots (RCQDs) isopropanol solution with quantum yield of 43.9 % have been synthesized using isopropanol as carbon source and solvent, N1-phenylbenzene-1,2,4-triamine as carbon and nitrogen source. The solvothermal synthesis was catalyzed surprisingly by SnO2 nanoparticles, the optimal synthesis temperature was lowered to 130 degrees C, and the optimal synthesis time was reduced to 1 h. Moreover, the RCQDs nanoparticles showed excellent solvatochromic properties. The maximum emission wavelength for RCQDs in N, N-dimethylformamide dilute solution blue shifted to 504 nm, and the maximum emission wavelengths for RCQDs in acetone, isopropanol, dimethyl sulfoxide and water solutions were in the range of 592 nm similar to 624 nm. The reason was investigated by the in-situ infrared absorption spectra. MnO4- ions could be selectively detected using RCQDs in PBS buffer solution (pH = 5.0), the linear range of MnO4- concentration was 0.1 mu M similar to 2.0 mu M. This work provides a new synthesis method of efficient red carbon quantum dots, and it supplies a friendly candidate for detection of MnO4- ions in water.

1-Chloro-2,4-dinitrobenzene (CDNB) is a highly allergenic compound, it is widely used for the quantitative detection of glutathione-s-transferase. This chemical in environment can cause serious effects on human health. High-performance liquid chromatography (HPLC) with ultra violet detector has been used to detect CNDB, and the limit of the detection (LOD) is 200 ng/ml. It is significant to find a simple and quick method to detect CDNB. It is still a challenge to detect CDNB from nitroaromatic compounds with alike structure of CDNB using luminescent probe method. In this work, yellow-green Bi2Se3 quantum dots (QDs) were firstly synthesized by solvothermal method, and its absolute luminescence quantum yield reached 13.8 +/- 0.2 %. Bi2Se3 QDs are environmentally friendly luminescent materials. The luminescence of the Bi2Se3 QDs solution was selectively quenched by CDNB molecules, CDNB could be selectively detected using Bi2Se3 QDs as luminescent probe. The linear range was 0.040 similar to 0.50 mu M, and the detection limit was 0.03 mu M. Some nitroaromatic compounds including 4-fluoro-1,2-dinitrobenzene (4-F-1,2-DNB), 1,3-dinitrobenzene (1,3-DNB), 2,6-dinitroaniline (2,6-DNA), p-chloronitrobenzene (p-CNB), 1-methyl-4-nitrobenzene (1-M-4-NB), 1-iodo-4-nitrobenzene (1-I-4-NB) and 1-(4-nitro-phenyl)-ethanone (4-NPE) did not interfere with the detection of CDNB. The detection of CDNB was interfered slightly only by 2,4-dinitroaniline (2,4-DNA) due to inner filter effect. The reason for the highly selective detection of CDNB using Bi2Se3 QDs was investigated detailed. The result provides a new sight for finding highly selective luminescent probe for organic chemicals based on the intermediate state formed between the surfaces of luminescent Bi2Se3 QDs and organic molecules through the characteristic second bond. Bi2Se3 QDs provide a new candidate for highly selective luminescent probe of CDNB with low limit of detection of 6.08 ng/ml.

Accurate detection of acetone (C3H6O) is essential for both environmental monitoring and noninvasive diabetes diagnosis. High-entropy alloys (HEAs) have been demonstrated as effective catalysts to replace noble metals for enhancing the gas-sensing performance of semiconductor metal oxides. However, HEAs tend to agglomerate at high temperatures, which severely limits their long-term stability and performance. To address this issue, a PtFeCoNiCuSn HEA was developed as a functional sensitizer for SnO2-based C3H6O sensors. The existence of Sn in the HEA structure enhances the interaction of HEA with SnO2 and prevents agglomeration under high-temperature conditions (≥300 °C), leading to improved stability and catalytic activity for C3H6O detection. The PtFeCoNiCuSn-SnO2-300 sensor exhibited increased sensitivity than its Sn-free HEA counterpart, along with shorter response and recovery times (6.5 s/10.5 s) at a working temperature of 230 °C, a clear response (Ra/Rg = 4.59@2 ppm), and a low detection limit down to 4 ppb for C3H6O. Moreover, it demonstrated stable long-term stability, with no significant response degradation (σ = 0.056) observed over a 63-day continuous test. The enhanced performance is attributed to the synergistic effects of the HEA's multielement composition and strong metal-support interaction, which strengthens electronic interaction and the activation of surface oxygen species. This study provides a framework for enhancing the interaction between HEAs and semiconductor metal oxides to further improve the gas-sensing properties of the latter.

3D organic-inorganic hybrid perovskite derived material FASnI3/SnO2 (HC(NH2)2SnI3/SnO2) is a good kind of gas sensing material for formaldehyde detection. However, it doesn't work well when the relative humidity is above 50 %. To solve this problem, a long-chain 2D perovskite (BA)2SnI4 ((C4H9NH3)2SnI4) is used to modify FASnI3/SnO2 composite due to its hydrophobic character. In this work, FASnI3/(BA)2SnI4 (HC(NH2)2SnI3/(C4H9NH3)2SnI4) with different ratios of the two materials are first synthesized by a solution method, and then these materials are partially oxidized by controlling the calcination temperature to obtain the FASnI3/(BA)2SnI4/SnO2 (HC(NH2)2SnI3/(C4H9NH3)2SnI4/SnO2) composite. The formaldehyde detection test showed that the response of FASnI3/SnO2 in medium humidity environment can be improved nearly two-thirds times, and the recovery time can be shortened from 183 s to 81 s. Moreover, the response value can reach to 32.5 at high humidity (78 RH%) and keeps unchanged after 24 h of continuous testing at this humidity. All these gas sensing properties improvement can be ascribed to the reason that the introduction of (BA)2SnI4 has led to the formation of the heterojunction and more vacancy oxygen. Of course, the hydrophobic character of FASnI3/(BA)2SnI4 also played an important role.

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Viologen has attracted much attention due to its sensitive chromic properties in response to external stimuli, especially its photochromic behavior. Herein,aviologenderivative,4PV2Br, was prepared based on our previous studies, which exhibited strong photoluminescence due to the introduction of the thiazolothiazole group but was silent to light, even under300 W UV light irradiation. By anion exchange with tetraphenylborate,a new viologenderivative,4PV2B(Ph)(4), was obtained, which not only exhibits strong fluorescence with a quantum yield of 69% and a lifetime of 1.93ns in solution but also exhibits sensitive photo chromism to UV light, even undersunlightwithin5 s. It is very sensitive to light and may become a potential excellent solar chromic material. It should be emphasized that the colored4PV2B(Ph)(4)radicalisparticularlystableand can maintain its coloring state in air for a long time, while vinegar vapor can cause it to fade in 2 s, giving it good color reversibility. The single-crystal structure before and after UV light excitations hows that UV light shortens the pipi distances between B(Ph)(4)anions and 4PV cations, which is beneficial to faster electron transfer between them and the formation of stable viologen radicals. Sensitive photo chromism accompanied by strong photoluminescence may endow 4PV2B(Ph)4 with potential application in information security and provide a good strategy to regulate the functionality of materials by regulating the counter anions of new viologen derivatives.

The nature of a built-in electric field within supported metal catalysts plays a crucial role in regulating gas adsorption and electron transfer during the gas-sensing process. Herein, we found an electron-supply redeployment phenomenon involving the reversal of direction of a built-in electric field between the metal palladium species and the outer S atoms in ZnS, resulting in a marked hydrogen sensing difference. It was found that Pd nanoparticles embedded into Pd NP-ZnS can induce spontaneous electron transfer from S atoms to Pd species to generate an electron-deficient sulfur (S(2-delta)-) surface. Conversely, atomically dispersed Pd species (Pd1-ZnS) prefer to generate electron-rich sulfur (S(2+delta)-) sites and thus reverse the built-in electric field. Theoretical calculations demonstrate that the electron-rich S (S(2+delta)-) surface can reduce the occupancy of antibonding orbitals in the S-Hads bond and enhance the bond energy of S-Hads, thus increasing the adsorption of hydrogen. Additionally, in situ Raman, ex situ X-ray photoelectron spectroscopy and DFT analysis demonstrate that S(2+delta)- sites in Pd1-ZnS samples can undergo strong electron transfer with hydrogen during the sensing process. Ultimately, Pd1-ZnS sensors exhibit extremely high response values (9.66/20 ppm) and fast response recovery times (5.1 s/1.8 s to 400 ppm) for hydrogen gas at a working temperature of 170 degrees C. The nature of a built-in electric field within supported metal catalysts plays a crucial role in regulating gas adsorption and electron transfer during the gas-sensing process.

Amorphous metal oxide semiconductor (MOS) materials are endowed with great promise to modulate electronic structures for gas-sensing performance improvement. However, the elevated-temperature requirement of gas sensors severely impedes the application of amorphous materials due to their low thermal stability. Here, a cationic-assisted strategy to tailor the Ni-O microenvironment in an amorphous-dominated Zn/NiO heterogeneous structure with high thermal stability was developed. It was found that 6 mol % Zn incorporation into amorphous NiO can effectively preserve the amorphous-dominated NiO phase even at high temperature. After calcination, the amorphous oxide can only be converted to crystals partly thus leading to the formation of amorphous/crystalline compounds, and the content of the amorphous phase can be adjusted by changing the calcination temperature. This amorphous/crystalline configuration can induce more electron transfer from Ni to Zn species, leading to the formation of active Ni delta+ (delta>2) centers. Ex situ XPS and in situ Raman spectroscopy studies proved that the generated Ni delta+ species pronouncedly promote the electron transfer during the H2S adsorption process. The amorphous/crystalline-6 mol % Zn/NiO sensor exhibits exceptional hydrogen sulfide response (2 ppm, 3.23), outstanding repeatability (as long as 5 weeks), and low limit of detection (as low as 50 ppb), surpassing most reported nickel-based gas sensors such as the crystal nickel oxide prepared in this work. The response and detection limit of the latter is only (2 ppm, 1.89) and (0.05 ppm) respectively. Our work thus opens up more opportunities for fundamental understanding and modulating of highly active amorphous sensing materials.

The luminescence stability of carbon quantum dots (CQDs) in air impedes their extensive applications. Ample -NH2 groups on the surface of a green carbon quantum dots (GCQDs) had high organic reactivity, the surface of GCQDs was modified with allyl functional groups through a simple surface substitution reaction (named as GCQD-A). The surface of the GCQD-A was continuously formed a thin organic shell by free radical copolymerization reaction with methyl methacrylate and styrene respectively, and they were named as GCQD@PMMA and GCQD@PS respectively. The allyl functional groups on the surface of GCQD-A, the shell composition of GCQD@PMMA and GCQD@PS were characterized by their 1H nuclear magnetic resonance (1H NMR) data and infrared adsorption spectra. The luminescence stabilities for GCQD@PMMA and GCQD@PS in air were greatly improved compared with that for the GCQDs. The work can provide a novel method to get stable luminescence of CQDs in air, and it will extend their application areas in solid state.

Reasonably constructing an atomic interface is pronouncedly essential for surface-related gas-sensing reaction. Herein, we present an ingenious feedback-regulation system by changing the interactional mode between single Pt atoms and adjacent S species for high-efficiency SO2 sensing. We found that the single Pt sites on the MoS2 surface can induce easier volatilization of adjacent S species to activate the whole inert S plane. Reversely, the activated S species can provide a feedback role in tailoring the antibonding-orbital electronic occupancy state of Pt atoms, thus creating a combined system involving S vacancy-assisted single Pt sites (Pt-Vs) to synergistically improve the adsorption ability of SO2 gas molecules. Furthermore, in situ Raman, ex situ X-ray photoelectron spectroscopy testing and density functional theory analysis demonstrate the intact feedback-regulation system can expand the electron transfer path from single Pt sites to whole Pt-MoS2 supports in SO2 gas atmosphere. Equipped with wireless-sensing modules, the final Pt1-MoS2-def sensors array can further realize real-time monitoring of SO2 levels and cloud-data storage for plant growth. Such a fundamental understanding of the intrinsic link between atomic interface and sensing mechanism is thus expected to broaden the rational design of highly effective gas sensors.

A new strategy is developed herein to improve the solid fluorescence of thiazolothiazole viologen by using the ZnCl42- cluster as a scaffold to hinder π-stacking. Importantly, the Cl···H bonds are formed in the solid state to sustain the framework and can be automatically dissociated when dissolved in H2O, thus having no impact on the strong emission in aqueous solution. As such, the first case of organic-inorganic viologen-zinc halide named 4PV·ZnCl4 was designed and synthesized, and a significant increase in photoluminescence quantum yield (ΦF) is realized from 4PV·2Br (ΦF = 0%) to 4PV·ZnCl4 (ΦF = 27.0%) in solid and from 97% to 98% in H2O. 4PV·ZnCl4 also displays pH stimuli-responsive naked-eye chromic behavior and photoluminescence with different coloring states and intensities. The multifunctional performance of 4PV·ZnCl4 provides a prerequisite for carrying different information, expanding their promising application in multilevel information encryption.

We report a type of micro-electro-mechanical system (MEMS) H2S gas sensors with excellent sensing performance at the ppb level (lowest detection limit is 5 ppb). The sensors were fabricated with ZnO/Co3O4 sensing materials derived from Zn/Co-MOFs by annealing at a suitable temperature of 500 °C. ZnO/Co3O4-500 exhibits the highest response when exposed to 10 ppb H2S gas at 120 °C, and the response/recovery times are 10 s/21 s. Moreover, it exhibits outstanding selectivity, long-term stability (retained 95% response after 45 days), and moisture resistance (only a minor fluctuation of 2% even at 90% RH). This can be ascribed to the fact that ZnO/Co3O4-500 has regular morphology, abundant oxygen vacancies (52.8%) and high specific surface area (96.5 m2 g-1). This work provides not only a high performance H2S MEMS gas sensor but also a systematic study of the effect of the annealing temperature on the sensing performance of ZnO/Co3O4 sensing materials derived from bimetal organic frameworks.

Bright yellow-green carbon quantum dots (YGCDs) were efficiently synthesized by a one-step hydrothermal method, and the absolute quantum yield of YGCDs reaches a high level in a short time compared with that using commonly reported solvothermal methods. The obtained carbon quantum dots could be used as a selective luminescent probe of folic acid in the range of 2.0 × 10-8 mol/l to 1.0 × 10-5 mol/l. This work is part of a special collection at Chemistry – An Asian Journal celebrating the 100th anniversary of Shanghai University (1922-2022), which commemorates the wonderful development process of the chemistry discipline of Shanghai University. More information on this study can be found in the Research Article by Bao-Li An, Jiaqiang Xu et al.

Bright yellow-green carbon quantum dots (YGCDs) have been successfully synthesized by a simple and efficient hydrothermal method. Their luminescent absolute quantum yield reached 30.0% in 4 h. Compared with commonly reported solvothermal methods, the synthesis time was reduced by more than 70% by using tin oxide nanoparticles as a catalyst. Moreover, the fluorescence of YGCDs could be selectively quenched by folic acid (FA) molecules, and the relative fluorescence intensities of F/F0 was fitted perfectly in line decay curve versus the concentration of FA in the range of 2.0×10-8  mol/l to 1.0×10-5  mol/l (R2 =0.9988). The detection limit of FA was below 2.0×10-8  mol/l, suggesting a promising fluorescent probe of folic acid.

Labelling various biological molecules with multi-color carbon quantum dots (CQDs) in the same scene has great potential application for investigating the relationship between those molecules. It is still a great challenge to regulate the color of CQDs. Ample –NH2 groups on the surface of green carbon quantum dots (GCQDs) were characterized and confirmed by 1H nuclear magnetic resonance (1H NMR) data. As–NH2 groups had high organic reactivity, the surface of GCQDs was designed and modified with several organic functional groups through a simple surface modification strategy of organic reactions. The surface band gap states of GCQDs were tuned gradually by the corresponding modified functional groups, and the emission colors of GCQDs were tuned from green to yellow-green, then to orange, and finally to red. All the emission spectra for these multicolor carbon quantum dots (M-CQDs) were excitation independent, and the lifetimes for the M-CQDs were mainly determined by the second electron decay process from the surface defect band states. The red-shift colors for the M-CQDs were ascribed to the emissions from their surface defect band states, and the luminescence mechanism had been investigated. This work opens up a novel synthesis strategy to regulate the emission colors of carbon quantum dots.