Recent Development of Gas–Solid Phase Chemiluminescence
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Serving as a classic and interesting strategy, gas–solid phase chemiluminescence (CL) has recently been a rapidly growing area where CL is emitted through chemical reactions between gas and solid reactants occurred on the surface of solid matter. This CL system provided a sensitive and simple spectral method for investigating gas–solid phase reactions while information on the rate constants, intermediate productions, surface states and reaction mechanisms of interaction could be acquired. Recent progresses mainly concentrate on development of new gas–solid phase CL systems and their practical applications. This review paper summarized main classifications, mechanisms and applications of gas–solid phase CL. The future prospects for gas–solid phase CL are discussed.
KeywordsGas–solid phase chemiluminescence Recent development Main classifications Mechanisms Applications
Chemiluminescence (CL) is the light emitted during chemical reactions where unstable products are evolved in the reaction process. These intermediates transformed from electronically excited to ground state with CL emission as energy release (> 45 cal/mol) . Since the fireflies and other luminescent organisms in the environment have been found, CL has aroused considerable interest for deeper research and application . Definitely, CL analysis has excellent advantages including high sensitivity, low background interference, highly responsive signals, safe operation process and portable equipment , which has been applied to detection towards the concentration of catalyst, reactant, CL inhibitor and enhancer . A great many articles have reported the applications of CL in environmental analysis , medical diagnosis , health management , food safety  and pharmaceuticals , etc.
Among numerous branches of CL systems, acting as a classic and interesting strategy, gas–solid phase CL has recently been a rapidly growing area. Such CL evolves in infrared, visible, and even in ultraviolet regions through chemical reactions between gas and solid reactants on the surface of solid matter. It acts as an indicator and monitor of gas–solid phase reactions to provide information during the process of reaction . Moreover, this strategy also enables investigations of gas–solid phase reactions through sensitive and simple spectral method . In addition, application of gas–solid phase CL has extended to gas-phase and solid-phase diagnose and detection due to its strong intensity of signals and unique property. Over decades of years of investigation and development, gas–solid phase CL has become an effective detection method in analytical chemistry. Recent progress mainly focuses on development of new gas–solid phase CL systems and their practical applications, while many interesting results have been reported. Obviously, the excellent sensitivity and intensity of gas–solid phase CL has made it a good candidate as a novel CL technology, which has revealed great potential for future analysis and test.
Considering the aforementioned properties, gas–solid phase CL have received considerable attentions in different areas of CL analysis. The present paper introduces the main classifications including O3-solid, O2-solid, “S-based”-solid, H2-solid and CO-solid CL systems. Besides, specific mechanisms, applications and future prospects of gas–solid phase CL are also covered.
2 Main Classifications of Gas–Solid Phase CL
2.1 O3-Solid System
2.1.1 O3–Ba System
2.1.2 O3–Ca System
2.1.3 O3-Alcohols, Phenols and Saccharides System
2.2 O2-Solid System
2.2.1 O2–Na System
O2 has always played as an effective oxidant towards all kinds of solid reactants for so many years. Researchers found that freshly cut Na would emit faint green light, which opens a new area of luminescence by Na metal. In 1931, Bowie  has investigated the color and intensity of CL emitted by solid Na existed in the air. He found that relevant intensity ranged from 3.5 to 10.5 × 10−7 lumens per square inch of the surface of Na and the CL spectrum was composed of a band of 5000–5300 Å. The CL intensity was too much low and corresponding color was green. He also investigated the mechanism within this process and believed that the CL has close relationship with formation of hydroxide from the moisture in the air where the breaking of H–O bond within a vaporous and polar molecule played as the main role .
2.2.2 O2-Fuel System
Investigation towards reactions of fuel will definitely acquire the information on ballistic property, which in return guides further modification and development. Campbell and Hulsizer  obtained the CL spectra of ammonium perchlorate composite solid propellant burned in the combustion zone. They found that A 2Σ+ electronic state of OH· was evolved in the flame, while these short-lived OH· also exist in the place very far from the surface of propellant. This system facilitated investigating the internal energy levels of ground and excited state during the process of combustion occurred at the surface of solid propellant.
2.2.3 O2-Polymer System
Research towards oxidation of polymer via CL strategy has enabled evaluation of oxidation mechanism, rate constant and further application of such process. Zlatkevich  utilized CL method for discussing heterogeneous oxidation of polypropylene. This work pointed out the erroneous evaluation of the activation energies and interpretation by previous articles. He also believed that experimental support is inadequate while the evolution of volatiles in the induction process also lacked sufficient consideration.
2.3 “S-Based” Solid System
2.3.1 S2-Solid Ar System
Kiljunen et al.  also investigated electronic structure and short-range recombination dynamics of S2 in solid Ar by classical molecular dynamics simulations. Result showed that S atom separated by closest distance of the lattice would recombine immediately even at 1 K with excitation energies of 2 eV or more to give excited S2.
2.3.2 SO-Solid Ar System
2.3.3 SO2-Solid Y2O2S–Eu System
2.4 H2-Solid System
2.4.1 H2-Solid Zn2SiO4–Mn System
2.4.2 H2-Solid ZnSCdS-Cu System
2.4.3 H2-Solid SiC System
2.5 CO-Solid System
3 Mechanisms of gas–solid phase CL
4 Applications of Gas–Solid Phase CL
A variety of equipment has been realized for detection and analysis of specific atoms or radicals based on gas–solid phase CL occurred at the surface of solid reactant, which laid foundation for obtaining information about rate constant, intermediate production, surface state and reaction mechanism of a CL system. What is more, this strategy could also be utilized in realistic determination to acquire real-time results of samples.
4.1 Chemical Sensor
A novel gas–solid phase chemical sensor based on CL strategy was devised by Karpov et al. . Serving as an effective complementary facility for traditional analytical techniques, this sensor has been applied to measurement towards the concentration of H, O and other gaseous chemical radicals. With the CL induced by Eley–Rideal recombination process took place, relevant property of such sensor has reached the sensitivity of 105 cm−3 with test time about 1 s.
4.2 CL Imaging
4.3 CL Spectrometer
Pronko and Chapman  have developed a microcomputer-controlled CL spectrometer with effective response and low cost, which could be utilized to study CL effect on the surface of materials in certain atmosphere. In addition, the CL spectra as a function of time and temperature could be recorded completely automatically. With the control of microcomputer, CL spectra in different regions could also be obtained.
5 Conclusions and Future Prospects
In this review article, we mainly concentrated on recent development of gas–solid phase CL. The main classifications including O3-solid, O2-solid, “S-based”-solid, H2-solid and CO-solid CL systems are summarized. In addition, specific mechanisms and applications of gas–solid phase CL in chemical sensor, imaging and spectrometer are also concluded. Results demonstrate that gas–solid phase CL system acts as a novel and effective platform for detection and analysis.
The investigation on gas–solid phase CL will create a new area by analyzing chemical reactions through gas–solid phase CL performance thus the information on rate constants, intermediate productions, surface states and reaction mechanisms could be acquired.
Moreover, gas–solid phase CL has provided a novel alternative in determining the concentration of gaseous atoms or radicals (H, O, S, etc.) which is complicated through traditional analytical methods. The unique characteristics of gas–solid phase CL like high sensitivity and strong CL intensity have made it an excellent tool in probing the emissive property of solid reactant in certain atmosphere.
Notably, gas–solid phase CL also eliminated the interference from solution where impurity and other reactants would inevitably influence the detection procedure and later deduction of mechanism. Serving as a simple CL process, gas–solid phase interaction facilitates fast identification and verification in real samples.
Although gas–solid phase CL also suffers from incomplete transformation due to surface reaction where most reactants in the bulk stay unreacted, the endeavor of establishment of new CL system and application in sample analysis will be invaluable to make contribution to further development of gas–solid phase CL system. With new achievement and challenges appearing continuously, research towards gas–solid phase CL remains a hot theme.
This work was supported by the National Natural Science Foundation of China (Nos. 21227006, 21435002, 81373373, 21621003). The authors declare no competing financial interests. All authors have given approval to the final version of the manuscript.
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