Microgravimetric Thermodynamic Modeling for Optimization of Chemical Sensing Nanomaterials

Abstract

On the basis of microgravimetric sensing data, an analytical modeling method is proposed for comprehensive evaluation and optimization of gas sensing or adsorbing related functional materials. Resonant microcantilever is loaded with the material to be evaluated for a gravimetric sensing experiment. With sensing isotherm curves obtained at different temperatures, key thermodynamic and kinetic parameters of the material, such as enthalpy ΔH°, Gibbs free energy, adsorption rate constant Ka, and coverage θ, etc., can be quantitatively extracted for optimal selection and design. On the basis of the gravimetric experiment, the modeling method is used on three sorts of trimethylamine sensing nanomaterials of mesoporous silica nanoparticles (MSNs). The COOH-functionalized material is clearly identified as the best sensing material among the three similar ones, thereby validating high accuracy of the proposed model. Broad applicability of the modeling method to other sensing materials and/or target gases is also experimentally confirmed, where sensing properties of a functionalized hyper-branched polymer to organophorous simulant of dimethyl methylphosphonate (DMMP) are still evaluated well. In addition to sensing materials, the gravimetric experiment-based modeling method can be expanded to other functional materials like moisture absorbents or detoxification agents. Water adsorbing experiment on KIT-5 mesoporous-silica is modeled, with the low -ΔH° value (i.e., low adsorption heat) result, indicating that the KIT-5 is a good adsorbent to humidity. Alternatively, the modeled high -ΔH° value (i.e., high reaction heat) shows promising usage of SBA-15 mesoporous-silica as detoxification material to hazardous organophorous chemicals. Therefore, the analytical modeling technology can be used for developing and evaluating new adsorbing materials for gas sensing, fixing, and detoxification applications.

Advanced Nanoporous Materials for Micro-Gravimetric Sensing to Trace-Level Bio/Chemical Molecules

“…Because functional organic groups have special interaction capability with some target molecules, surface graft of organic group is considered one of the most effective methods to improve selectivity. For example, there is a special interaction between carboxylic group (-COOH) and ammonia molecule [34,55,56]. Based on the surface modification scheme, the mesoporous silica can be pre-functionalized with some specific organic groups to become a specific micro-gravimetric sensing material.…”

“…Herein, the interference from other natural gases such as CO 2 can be ignored, as there are few kinds of basic gas (except for ammonia/amines) existing in environment [34,55]. Using CES (carbomethoxysilanetriol, sodium salt, 25 wt% in water) as the key precursor, the CMS sensing material can be prepared with post-grafting method.…”

Hyper-branch sensing polymer batch self-assembled on resonant micro-cantilevers with a coupling-reaction route

“…Although some special coating techniques like ink-jet spotting and tiny-capillary incubation under optical microscope have been used, manual loading is really a difficult task to secure uniform sensing performance within a whole run of fabricated sensors [13,[19][20][21][22]. In our lab, a commercially available micro-manipulator equipped with a labmade capillary is employed to load the sensing material onto the desired micro-region of the cantilever [23][24][25][26][27][28][29]. With the help of this special tool, various sensing materials like functionalized mesoporous silica, sensing polymer and Au-NPs/grapheme-oxide hybrid have been precisely coated onto resonant cantilevers to construct high-sensitivity gas sensors [23][24][25][26][27][28][29].…”

“…In our lab, a commercially available micro-manipulator equipped with a labmade capillary is employed to load the sensing material onto the desired micro-region of the cantilever [23][24][25][26][27][28][29]. With the help of this special tool, various sensing materials like functionalized mesoporous silica, sensing polymer and Au-NPs/grapheme-oxide hybrid have been precisely coated onto resonant cantilevers to construct high-sensitivity gas sensors [23][24][25][26][27][28][29]. Unfortunately, such an approach is still a one-by-one method that suffers from several drawbacks like time-consuming, labor-intensive, inconsistent and irreproducible.…”

Quantitatively extracted Gibbs free-energy (ΔG) as criterion to determine working temperature range of gas sensing-material

“…Based on the adsorption between mesoporous silica nanoparticles (MSNs) and organophosphorus, MSNs shows potential for developed as toxic organophosphorus detoxification materials. Herein, a lab-made resonant microcantilever is used to real time record molecule-uptakes of the loaded material by reading the frequency-shift signals at different temperatures (T), thereby extracting ΔG°, ΔH° and ΔS° by using the method as we described previously [4]. With the extracted ΔH° and ΔS°, the value of T max can be work out based on the criterion of ΔG(T)=ΔH-TΔS≥0.…”