Kinetics of liquid phase batch adsorption experiments

Efficient recovery of gold from solution with a thiocyanate-modified Zr-MOF: adsorption properties and DFT calculations

The design and development of new large-capacity and selective materials for extracting rare precious metals via electronic waste is practically essential. In this paper, a new efficient UiO-66-NCS has been obtained as a consequence of the modification of the classical Zr-MOF (UiO-66-NH2), and its ability to recover gold has been investigated. These batch results adequately illustrated that UiO-66-NCS exhibited good adsorption capacity (675.5 mg g-1) and exceptional selectivity. In addition, UiO-66-NCS achieved faster adsorption equilibrium times of about 120 min. Adsorption kinetics and isotherms demonstrated that the pseudo-second-order adsorption scheme and a Langmuir-type procedure were shown by the adsorption of Au(III) on UiO-66-NCS. Characterized by pH effect experiments, TEM, XRD, and XPS, the adsorption of UiO-66-NCS with Au(III) relies on coordination, which further results in reduction, and the generated Au(0) is uniformly dispersed in the MOF. The adsorbent has considerable advantages for cyclic regeneration. Finally, DFT fitting results showed that the adsorption binding energy of UiO-66-NCS with [AuCl4]- was -8.63 kcal mol-1 for the adsorption process. UiO-66-NCS is likely to be an ideal substance for gold recovery.

Synergistic sono-adsorption and adsorption-enhanced sonochemical degradation of dyes in water by additive manufactured PVDF-based materials

The present study proposes the first mechanistic model accounting for the most meaningful physico-chemical phenomena taking place in liquid phase adsorption processes under ultrasound. Initially, this study was aimed at developing an easy-to-make and easy-to-recover piezocatalyst for the degradation of RhB in water by combining the high piezocatalytical performance of BaTiO3 with a compatible piezoelectric support such as PVDF, manufactured by a customised additive manufacturing - direct ink writing system with in-situ poling. However, initial results showed that the resulting PVDF-BaTiO3 composite slabs performed worse than BaTiO3 piezocatalysts on their own, and that poling did not have any effect on their performance (82% RhB removal after 2 h when using either poled or unpoled PVDF-BaTiO3 composite slabs compared to 92% RhB removal after 2 h in presence of BaTiO3 piezocatalysts). Further investigation with pure PVDF materials demonstrated that, instead of piezocatalysis, synergistic ultrasound-assisted adsorption and sonochemical degradation were taking place, enabling the removal of >95% of the dye within 40 min of ultrasound treatment in the presence of 4 g L-1 of additive manufactured PVDF slabs. The results of this study and their evaluation with the mechanistic model proposed for liquid phase adsorption under ultrasound suggest that the adsorption of RhB on additive manufactured PVDF slabs was enhanced by the structure, higher specific surface ratio and higher volume of mesopores achieved through the 3D-printing process, as well as the minimisation of film resistance to mass transport due to ultrasound. Moreover, adsorption on additive manufactured PVDF enhanced the sonochemical degradation of the dye due to its high concentration in the adsorbed phase. This study demonstrates that adsorption processes, especially in the presence of PVDF materials, may be significantly more important in piezocatalysis than what has been reported to date, to the point that the synergistic combination of sono-adsorption and sonochemical degradation in presence of additive-manufactured PVDF slabs may be enough to achieve high removal rates of dyes in water.

Molecular Diffusion in Nanoreactors' Pore Channel System: Measurement Techniques, Structural Regulation, and Catalytic Effects

Nanoreactors, as a new class of materials with highly enriched and ordered pore channel structures, can achieve special catalytic effects by precisely identifying and controlling the molecular diffusion behavior within the ordered pore channel system. Nanoreactors-driven molecular diffusion within the ordered pore channels can be highly dependent on the local microenvironment in the nanoreactors' pore channel system. Although the diffusion process of molecules within the ordered pore channels of nanoreactors is crucial for the regulation of catalytic behaviors, it has not yet been as clearly elucidated as it deserves to be in this study. In this review, fundamental theory and measurement techniques for molecular diffusion in the pore channel system of nanoreactors are presented, structural regulation strategies of pore channel parameters for controlling molecular diffusion are discussed, and the effects of molecular diffusion in the pore channel system on catalytic reactivity and selectivity are further analyzed. This article attempts to further develop the underlying theory of molecular diffusion within the theoretical framework of nanoreactor-driven catalysis, and the proposed perspectives may contribute to the rational design of advanced catalytic materials and the precise control of complex catalytic kinetics.

An Exploratory Study of Hydrochar as a Matrix for Biotechnological Applications

This paper explores the potentialities of hydrochar in protein separation and enzyme immobilization for non-energy biorefinery applications of hydrothermal carbonization. An innovative experimental procedure monitors soluble protein-hydrochar interactions and enzymatic reactions in a continuously stirred tank reactor. The hydrochar comes from hydrothermal carbonization of silver fir (200 °C, 30 min, 1/7 solid/water ratio) and standard activation (KOH, oven, 600 °C). Bovine serum albumin, a non-active, globular protein, was adsorbed at ≤3300 mg/g. Sip's isotherms fitted data well (R2 = 0.99999). The immobilization used a commercial β-glucosidase, which catalyzes the hydrolysis of cellobiose to glucose, a bottleneck of the cellulose to fermentable sugar bioconversion network due to the fast enzyme deactivation. The hydrochar adsorbed ≤26 w/w% of enzyme. The heterogeneous biocatalyst operational stability was 24 times that of the soluble one. The results encourage further investigations and foreshadow process schemes coupling hydrothermal carbonization and industrial bioconversions.

Flower-like Thiourea-Formaldehyde Resin Microspheres for the Adsorption of Silver Ions

Around a quarter of annual worldwide silver consumption comes from recycling. It remains a primary target for researchers to increase the silver ion adsorption capacity of the chelate resin. Herein, a series of flower-like thiourea-formaldehyde microspheres (FTFM) possessing diameters of 15-20 μm were prepared via a one-step reaction under acidic conditions, and the effects of the monomer molar ratio and reaction time on the micro-flower morphology, specific surface area, and silver ion adsorption performance were explored. The nanoflower-like microstructure showed the maximum specific surface area 18.98 ± 0.949 m²/g, which was 55.8 times higher than that of the solid microsphere control. As a result, the maximum silver ion adsorption capacity was 7.95 ± 0.396 mmol/g, which was 10.9 times higher than that of the control. Kinetic studies showed that the equilibrium adsorption amount of FT₁F₄M was 12.61 ± 0.016 mmol/g, which was 11.6 times higher than that of the control. Additionally, the isotherm study of the adsorption process was performed, and the maximum adsorption capacity of FT₁F₄M was 18.17 ± 1.28 mmol/g, which was 13.8 times that of the control according to the Langmuir adsorption model. Its high absorption efficiency, convenient preparation strategy, and low cost recommend FTFM bright for further use in industrial applications.

Synthesis of Titanium Ion Sieves and Its Application for Lithium Recovery from Artificial Indonesian Geothermal Brine

Indonesia is one of the countries in the world that has been utilizing geothermal as a renewable energy source to generate electricity. Depending on the geological setting, geothermal brine possesses critical elements worthwhile to extract. One of the critical elements is lithium which is interesting in being processed as raw material for the battery industries. This study thoroughly presented titanium oxide material for lithium recovery from artificial geothermal brine and the effect of Li/Ti mole ratio, temperature, and solution pH. The precursors were synthesized using TiO2 and Li2CO3 with several variations of the Li/Ti mole ratio mixed at room temperature for 10 min. The mixture of 20 g of raw materials was put into a 50 mL crucible and then calcined in a muffle furnace. The calcination temperature in the furnace was varied to 600, 750, and 900 °C for 4 h with a heating rate. of 7.55 °C/min. After the synthesis process, the precursor is reacted with acid (delithiation). Delithiation aims to release lithium ions from the host Li2TiO3 (LTO) precursor and replace it with hydrogen ions through an ion exchange mechanism. The adsorption process lasted for 90 min, and the stirring speed was 350 rpm on a magnetic stirrer with temperature variations of 30, 40, and 60 °C and pH values of 4, 8, and 12. This study has shown that synthetic precursors synthesized based on titanium oxide can absorb lithium from brine sources. The maximum recovery obtained at pH 12 and a temperature of 30 °C was 72%, with the maximum adsorption capacity obtained was 3.55 mg Li/gr adsorbent. Shrinking Core Model (SCM) kinetics model provided the most fitted model to represent the kinetics model (R2 = 0.9968), with the constants kf, Ds, and k, are 2.2360 × 10-9 cm/s; 1.2211 × 10-13 cm2/s; and 1.0467 × 10-8 cm/s.

Graphical Abstract

Analysis of commonly used batch adsorption kinetic models derived from mass transfer-based modelling

Modelling of liquid-solid batch adsorption based on mass transfer and conservation equations results in differential equations that may have or not an analytical solution. Even when analytical solutions are available, several simplified models can be considered for evaluating kinetic data of batch adsorption experiments. However, these simplified models are commonly used regardless of the premises considered in its development, and the analysis of the kinetic experiments based on these simplified models may be severely compromised. For this reason, this work presents a detailed development of the phenomenological models, and the hypotheses considered in its development are clearly stated. Typical simplified models derived from the phenomenological ones are obtained, and the conditions considered in the simplification are critically assessed. It was observed that the simplified models fail mainly for considering the concentration of the bulk phase constant over time or considering a linear adsorption isotherm. It must be emphasised that even when phenomenological models must be solved through numerical procedures, its use must be preferred, since the agreement with model premises and experimental conditions are closer, ensuring the quality of the kinetic data analysis.

Why Is the Linearized Form of Pseudo-Second Order Adsorption Kinetic Model So Successful in Fitting Batch Adsorption Experimental Data?

There is a vast amount of literature devoted to experimental studies on adsorption from liquids examining the adsorption potential of various adsorbents with respect to various solutes. Most of these studies contain not only equilibrium but also kinetic experimental data. The standard procedure followed in the literature is to fit the kinetic experimental adsorption data to some models. Typically empirical models are employed for this purpose and among them, the pseudo-first and pseudo-second order kinetic models are the most extensively used. In particular, the linear form of their integrated equations is extensively employed. In most cases, it is found that the pseudo-second order model is not only better than other models but also leads to high fitting quality. This is rather strange since there is no physical justification for such a model, as it is well accepted that adsorption kinetics is dominated by a diffusion process. In the present work, it will be shown through examples and discussion that the success of the linearized pseudo-second order model in fitting the data is misleading. Specific suggestions on appropriate adsorption data treatment are given.

Photocatalytic Performance of Carbon-Containing CuMo-Based Catalysts under Sunlight Illumination

Carbon-doped nanostructured CuMo-based photocatalysts were prepared by solvothermal synthesis. Two thermal treatments—oxidative and inert atmosphere—were used for the synthesis of the catalysts, and the influence of spherical carbon structures upon the crystalline phases on the photocatalytic activity and stability was studied. XRD showed the catalysts are nanostructured and composed by a mixture of copper (Cu, Cu2O, and CuO) and molybdenum (MoO2 and MoO3) crystalline phases. The catalysts were used for the degradation of yellow 5 under solar light. A remarkable leaching of Mo both in dark and under solar irradiation was observed and quantified. This phenomenon was responsible for the loss of photocatalytic activity for the degradation of the dye on the Mo-containing series. Conversely, the Cu-based photocatalysts were stable, with no leaching observed after 6 h irradiation and with a higher conversion of yellow 5 compared with the Mo- and CuMo series. The stability of Cu-based catalysts was attributed to a protective effect of spherical carbon structures formed during the solvothermal synthesis. Regarding the catalysts’ composition, sample Cu4-800-N2 prepared by pyrolysis exhibited up to 4.4 times higher photoactivity than that of the pristine material, which is attributed to a combined effect of an enhanced surface area and micropore volume generated during the pyrolytic treatment due to the presence of the carbon component in the catalyst. Scavenger tests have revealed that the mechanism for tartrazine degradation on irradiated Cu-based catalysts involves successive attacks of •OH radicals.

Efficacy of an organically modified bentonite to adsorb 2,4-dichlorophenoxyacetic acid (2,4-D) and prevent its phytotoxicity

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is widely used due to it selective action, and preferential control of dicotyledonous weeds affecting cereal crops. Physiological responses of sensitive dicotyledonous plants to 2,4-D include growth retardation, senescence, and cell death. Due to soil and water contamination by agricultural practices, 2,4-D constitutes a potential risk to non-target plant species. In this work, the potential advantage of using organic modified bentonite (Bent) to adsorb 2,4-D and therefore mitigate damage produced by this herbicide on sensitive not-target vegetable species was investigated. Dodecylamine (DDA) was used as an organic modifier to change the hydrophilic nature of Bent into an organophilic matrix. The adsorption performances of 2,4-D by Bent-DDA were analyzed. The maximum adsorptions of 2,4-D (22.1 mg/L) from aqueous solution containing 1.0 or 2.5 mg/mL Bent-DDA were 40 and 80 %, respectively. The physical interaction of Bent-DDA with 2,4-D was characterized by Wide Angle X-ray Scattering (WAXS) and thermogravimetric analysis (TGA). The biological functionality of Bent-DDA matrix as 2,4-D adsorbent was tested in a bioassay in the Arabidopsis thaliana plant model system. The primary root growth of Arabidopsis seedlings is strongly inhibited by low concentrations of 2,4-D. Arabidopsis seedlings submitted to Bent-DDA pre-treated herbicide aqueous solution showed similar root growth than 2,4-D non-treated seedlings. Finally, the ability of Bent-DDA to prevent 2,4-D phytotoxicity was exploratory investigated in lettuce plants. Lettuce plants pre-treated with 20 μg/mL Bent-DDA showed reduced sensitivity to 2,4-D including an increment on chlorophyll content and biomass compared with non-treated plants. Our findings revealed a promising scenario for the application of Bent-DDA as an effective adsorbent of 2,4-D at productive scale.

Nanoconfinement and mass transport in metal-organic frameworks

The ubiquity of metal-organic frameworks in recent scientific literature underscores their highly versatile nature. MOFs have been developed for use in a wide array of applications, including: sensors, catalysis, separations, drug delivery, and electrochemical processes. Often overlooked in the discussion of MOF-based materials is the mass transport of guest molecules within the pores and channels. Given the wide distribution of pore sizes, linker functionalization, and crystal sizes, molecular diffusion within MOFs can be highly dependent on the MOF-guest system. In this review, we discuss the major factors that govern the mass transport of molecules through MOFs at both the intracrystalline and intercrystalline scale; provide an overview of the experimental and computational methods used to measure guest diffusivity within MOFs; and highlight the relevance of mass transfer in the applications of MOFs in electrochemical systems, separations, and heterogeneous catalysis.

Characterization of pruned tea branch biochar and the mechanisms underlying its adsorption for cadmium in aqueous solution

In the present study, discarded pruned tea branch was used to prepare a new biochar, and the physicochemical properties and adsorption characteristics were investigated by characterization and batch experiments. With increasing pyrolysis temperature from 400 to 800 °C, the yield, specific surface area, and acidic functional groups had significant differences. The optimum adsorption conditions were determined as pH = 6 and dosage of 2 g L^-1. The pseudo-second-order kinetic and Langmuir isothermal model could fit well to the adsorption data, which showed that the adsorption process was dominated by monolayer chemical adsorption. The highest adsorption property (74.04 mg g^-1) was obtained by the pyrolysis of tea branch biochar (TBB) at 700 °C owing to the adsorption mechanisms, including surface complexation, precipitation, metal ion exchange, and Cd²⁺-π interaction. After five cycles of desorption, biochar still showed superior adsorption (80%). Hence, the TBB acted as a regenerable adsorbent for treating Cd²⁺-containing wastewater.

Engineering of UiO-66-NH2 as selective and reusable adsorbent to enhance the removal of Au(III) from water: Kinetics, isotherm and thermodynamics

Efficient removal of gold ions from wastewater has become a hot research topic. A new metal-organic framework material (PAR-UiO-66) was prepared by post-modification of UiO-66-NH₂. A series of characterizations proved the successful preparation of PAR-UiO-66. The batch adsorption experiment was carried out. Under the room temperature (298 K) of and pH 4.0, the optimal adsorption capacity of PAR-UiO-66 for gold ions was 683.45 mg/g, which was an increase of 426.8 mg/g compared with that of UiO-66-NH₂. The adsorption of gold ions on PAR-UiO-66 accords with pseudo-second-order kinetics and Langmuir isotherm modles. The adsorption process was endothermic and spontaneous. PAR-UiO-66 has good selectivity and still has 92.5% adsorption efficiency after five repeated adsorptions. The adsorption mechanism is electrostatic attraction, reduction and chelation.