Key Takeaways & Executive Findings
- •• Uniform-sized hollow mesoporous silica spheres form colloidal photonic crystals for gas sensing. • 'Nanoreceptors' have been introduced for increasing the sensing sensitivity and specificity. • A chloroform gas sensor is created with a sensitivity of 0.79 nm ppm−1 with a limit of detection of 3.22 ppm, which are the best reported values in fast-response chloroform vapor sensors without multi-signal assistance. • The sensor exhibits fast response (7.5 s positive, 9 s negative) and stable performance across a wide range of humidity (20–85% RH) and temperature (25–55 °C).
Abstract
Chloroform and other volatile organic pollutants have garnered widespread attention from the public and researchers, because of their potential harm to the respiratory system, nervous system, skin, and eyes. However, research on chloroform vapor sensing is still in its early stages, primarily due to the lack of specific recognition motif. Here we report a mesoporous photonic crystal sensor incorporating carbon dots-based nanoreceptor (HMSS@CDs-PCs) for enhanced chloroform sensing. The colloidal PC packed with hollow mesoporous silica spheres provides an interconnected ordered macro-meso-hierarchical porous structure, ideal for rapid gas sensing utilizing the photonic bandgap shift as the readout signal. The as-synthesized CDs with pyridinic-N-oxide functional groups adsorbed in the hollow mesoporous silica spheres are found to not only serve as the chloroform adsorption sites, but also a molecular glue that prevents crack formation in the colloidal PC. The sensitivity of HMSS@CDs-PCs sensor is 0.79 nm ppm−1 and an impressively low limit of detection is 3.22 ppm, which are the best reported values in fast-response chloroform vapor sensor without multi-signal assistance. The positive response time is 7.5 s and the negative response time 9 s. Furthermore, relatively stable sensing can be maintained within a relative humidity of 20%–85%RH and temperature of 25–55 °C. This study demonstrates that HMSS@CDs-PCs sensors have practical application potential in indoor and outdoor chloroform vapor detection.
1. Introduction
Chloroform and other volatile organic pollutants have garnered widespread attention from the public and researchers, because of their potential harm to the respiratory system, nervous system, skin, and eyes. However, research on chloroform vapor sensing is still in its early stages, primarily due to the lack of specific recognition motif. Photonic crystal (PC) sensors offer a promising platform for gas detection, as both qualitative and quantitative detection of gas can be achieved by measuring the shift in the diffraction peak.
However, in practical outdoor applications for detecting chloroform vapor, the sensitivity and selectivity of PC sensors are often poor, due to the lack of specific receptors to the analytes. Using conventional chemical functional groups lacks the specificity, while employing protein-based receptors could fall short in stability and cost-effectiveness. In this work, we have introduced nanoparticle-based 'receptors' for increasing the sensing sensitivity and specificity. Carbon dots (CDs) are nanomaterials composed of carbon skeletons, typically comprising a mixture of hybrid graphite carbon and amorphous carbon, with particle sizes below 10 nm and a rich, tunable variety of surface functional groups. In previous studies, CDs have demonstrated rapid photo-generated electron transfer capabilities, exceptional fluorescence properties, and have been successfully employed as efficient electron acceptors and donors. The functional groups on CDs assume a three-dimensional spatial arrangement, which provides additional spatial confinement for sensing specificity. Importantly, the dimension of CDs matches perfectly with mesopores (2–50 nm); therefore, CDs can be embedded in mesopores, functioning as 'nanoreceptors.'
Another challenge in wet chemistry-based fabrications is to form large-area, uniform colloidal PC films. During the self-assembly process of colloidal particles to form PC films, cracks are often prevalent. These cracks and other structural defects significantly impact the performance of the sensors. Though these defects may play a role of waveguides in some cases, the randomness of crack appearance significantly affects the consistency of sensing signals, which requires new strategies for circumventing crack formation. Additionally, hierarchically ordered CPC sensors have the flexibility in constituent particle morphology and chemistry design that can accommodate different functional group modifications, providing unique advantages in gas detection selectivity.
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Junchen Liu, Ji Liu, Zhipeng Li, Liupeng Zhao, Tianshuang Wang, Xu Yan, Fangmeng Liu, Xiaomin Li, Qin Li, Peng Sun, Geyu Lu, Dongyuan Zhao (2024). Carbon Dots-Modified Hollow Mesoporous Photonic Crystal Materials for Sensitivity- and Selectivity-Enhanced Sensing of Chloroform Vapor. Nano-Micro Letters. https://doi.org/10.1007/s40820-024-01598-9
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Frequently Asked Questions
What is the main innovation of this study?
The study introduces carbon dots-based nanoreceptors into hollow mesoporous silica photonic crystals, enhancing both sensitivity and selectivity for chloroform vapor sensing, achieving the best reported performance in fast-response sensors without multi-signal assistance.
What are the key performance metrics of the sensor?
The sensor exhibits a sensitivity of 0.79 nm ppm−1, a limit of detection of 3.22 ppm, positive response time of 7.5 s, and negative response time of 9 s, with stable operation across 20–85% RH and 25–55 °C.
How do carbon dots improve the sensing performance?
Carbon dots with pyridinic-N-oxide functional groups serve as specific adsorption sites for chloroform, enhancing sensitivity and selectivity. They also act as a molecular glue, preventing crack formation in the colloidal photonic crystal, improving structural integrity and signal consistency.
What is the practical application potential of this sensor?
The sensor shows practical potential for indoor and outdoor chloroform vapor detection due to its high sensitivity, selectivity, fast response, and stability under varying humidity and temperature conditions.
What is the significance of the photonic crystal structure?
The hollow mesoporous silica spheres form a colloidal photonic crystal with an interconnected ordered macro-meso-hierarchical porous structure, enabling rapid gas diffusion and a measurable photonic bandgap shift as the sensing signal.
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