In Situ Quantitative Monitoring of Adsorption from Aqueous Phase by UV-vis Spectroscopy: Implication for Understanding of Heterogeneous Processes

Abstract

The development of in situ techniques to quantitatively characterize the heterogeneous reactions is essential for understanding physicochemical processes in aqueous phase. In this work, a new approach coupling in situ UV-vis spectroscopy with a two-step algorithm strategy is developed to quantitatively monitor heterogeneous reactions in a compact closed-loop incorporation. The algorithm involves the inverse adding-doubling method for light scattering correction and the multivariate curve resolution-alternating least squares (MCR-ALS) method for spectral deconvolution. Innovatively, theoretical spectral simulations are employed to connect MCR-ALS solutions with chemical molecular structural evolution without prior information for reference spectra. As a model case study, the aqueous adsorption kinetics of bisphenol A onto polyamide microparticles are successfully quantified in a one-step UV-vis spectroscopic measurement. The practical applicability of this approach is confirmed by rapidly screening a superior adsorbent from commercial materials for antibiotic wastewater adsorption treatment. The demonstrated capabilities are expected to extend beyond monitoring adsorption systems to other heterogeneous reactions, significantly advancing UV-vis spectroscopic techniques toward practical integration into automated experimental platforms for probing aqueous chemical processes and beyond.

Keywords: UV–vis spectroscopy; adsorption; computational chemistry; heterogeneous reaction; multivariate curve resolution.

Figure 1

Monitoring of the aqueous adsorption kinetics of BPA (40 mg L⁻¹) onto suspended polyamide microparticles (10.45 g L⁻¹) in water. a) Schematic of the absorption spectra extraction method. b–d) UV–vis spectral kinetic dataset of b) reflectance, c) transmittance, and d) absorption coefficient monitored 20 times at 1 min time intervals.

Figure 2

Absorption spectra deconvolution of the kinetic UV–vis absorption spectra. a) Schematic of the MCR‐ALS method. b) Eigenvalues related to the pure species calculated through singular value decomposition. c) Pure spectral profiles obtained by two‐component MCR‐ALS decomposition in two parallel tests. d) Corresponding spectral weight factor obtained by two‐component MCR‐ALS decomposition.

Figure 3

Computational spectroscopic simulation. a,b) Molecular dynamic simulations of 10 BPA molecules in water environments (a) and multiple BPA molecules, polyamide units in water environments (b). c,d) Density functional theory simulation of the free BPA molecules and the optimized BPA‐polyamide structures. e,f) Twenty excitation states and the fitted theoretical UV–vis spectra calculated by time‐dependent density functional theory calculation of aqueous BPA and adsorbed BPA. g,h) Natural transition orbital analysis of aqueous BPA molecules and adsorbed BPA.

Figure 4

Quantitative performance validation of the aqueous adsorption of BPA onto suspended polyamide microparticles. a) Linear regression analysis comparing the in situ spectral method (estimated) with the ex situ batch sampling method (reference). b) Bland–Altmann plot analysis.

Figure 5

Practical applications of the approach for aqueous adsorption quantification of CIP (20 mg L⁻¹) onto commercial adsorbents (200 mg L⁻¹). a,c) In situ spectroscopic monitoring of the aqueous adsorption of CIP onto a) diatomite and c) carclazyte. b,d) Adsorption kinetics estimated by the proposed method for the aqueous adsorption of CIP onto b) diatomite and d) carclazyte.