Insights into deactivation mechanism of sulfonated carbonaceous solid acids probed by cellulose hydrolysis

Sulfonic acid functionalized cellulose-derived (nano)materials: Synthesis and application

The preparation/application of heterogeneous (nano)materials from natural resources has currently become increasingly fascinating for researchers. Cellulose is the most abundant renewable polysaccharide on earth. The unique physicochemical, structural, biological, and environmental properties of this natural biopolymer have led to its increased application in many fields. The more desirable features of cellulose-based (nano)materials such as biodegradability, renewability, biocompatibility, cost-effectiveness, simplicity of preparation, environmentally friendly nature, and widespread range of applications have converted them into promising compounds in medicine, catalysis, biofuel cells, and water/wastewater treatment processes. Functionalized cellulose-based (nano)materials containing sulfonic acid groups may prove to be one of the most promising sustainable bio(nano)materials of modern times in the field of cellulose science and (nano)technology owing to their intrinsic features, high crystallinity, high specific surface area, abundance, reactivity, and recyclability. In this review, the developments in the application of sulfonated cellulose-based (nano)materials containing sulfonic acid (-SO3H) groups in catalysis, water purification, biological/biomedical, environmental, and fuel cell applications have been reported. This review provides an overview of the methods used to chemically modify cellulose and/or cellulose derivatives in different forms, including nanocrystals, hydrogels, films/membranes, and (nano)composites/blends by introducing sulfonate groups on the cellulose backbone, focusing on diverse sulfonating agents utilized and substitution regioselectivity, and highlights their potential applications in different industries for the generation of alternative energies and products.

Insights into Preparation Methods and Functions of Carbon-Based Solid Acids

With the growing emphasis on green chemistry and the ecological environment, researchers are increasingly paying attention to greening materials through the use of carbon-based solid acids. The diverse characteristics of carbon-based solid acids can be produced through different preparation conditions and modification methods. This paper presents a comprehensive summary of the current research progress on carbon-based solid acids, encompassing common carbonization methods, such as one-step, two-step, hydrothermal, and template methods. The composition of carbon source material may be the main factor affecting its carbonization method and carbonization temperature. Additionally, acidification types including sulfonating agent, phosphoric acid, heteropoly acid, and nitric acid are explored. Furthermore, the functions of carbon-based solid acids in esterification, hydrolysis, condensation, and alkylation are thoroughly analyzed. This study concludes by addressing the existing drawbacks and outlining potential future development prospects for carbon-based solid acids in the context of their important role in sustainable chemistry and environmental preservation.

Role of acidic hydrochar on dechlorination of waste PVC in high temperature hydrothermal treatment and fuel properties enhancement of solid residues

In this study, the chlorine mitigation from waste polyvinyl chloride (WPVC) during high temperature co-hydrothermal treatment (co-HTT) and the properties of the generated solid products were assessed. WPVC was co-fed with acidic hydrochar (AHC), which was produced via hydrothermal carbonization of pineapple waste in the presence of citric acid water solution. High temperature co-HTT experiments were performed at 300-350 °C, 0.25-4 h of reaction time, and 0-20 wt% AHC loading. Co-HTT solid products (co-HTT_SP) were characterized via proximate analysis, ultimate analyses, combustion analysis, and ash analysis. The results show that the addition of 5% AHC enhances the dechlorination efficiency (DE) of WPVC from 89.35% to 97.66% at 325 °C and 0.5 h. The highest DE, reaching 99.46%, was achieved at 350 °C and 1 h in the presence of 5 wt% AHC. Furthermore, loading 5% AHC improved the higher heat value (HHV) of the solid products from 23.09 to 31.25 MJ/kg at 325 °C and 0.5 h. The maximum HHV (34.77 MJ/kg) of a solid product was achieved at 350 °C, 4 h, in the presence of 5 wt% of AHC. The co-HTT solids shown low slagging indices, fouling indices, alkali indices, and medium chlorine contents. These findings support the viability of WPVC conversion into clean solid fuel via co-HTT.

Effect of Acidic Hydrochar on Plastic Crude Oil Produced from Hydrothermal Liquefaction of Waste PVC

In this study, the effect of hydrothermal liquefaction (HTL) of waste PVC was investigated in the presence of acidic hydrochar. The hydrochar was prepared by hydrothermal carbonization of pineapple waste at 250 °C and at 1 h in the presence of citric acid. Hydrochar was acidic, stable, and porous and contained acidic functional groups. Hydrochar was co-fed with PVC during HTL to enhance HTL conversion and quality of the plastic crude oil. HTL experiments were performed at 300–350 °C, 0.25–4 h of reaction times, and 0–20 wt% hydrochar-to-PVC ratio. The plastic crude oil was separated from the solid residue to evaluate HTL conversion and to analyze elemental compositions, boiling point distribution, alteration of chemical bonds, and chemical compositions. The results showed that acidic hydrochar enhances HTL conversion with a maximum value of 28.75 at 5 wt% hydrochar content at 350 °C and 0.5 h. Furthermore, plastic crude oils contained no chloride but contained significantly high carbon and hydrogen, resulting in a higher heating value of up to 36.43 MJ/kg. The major component of the plastic crude oil was 3, 5 dimethylphenol produced ranging from 61.4 to 86.4% (percentage of total identified area) according to gas chromatography mass spectroscopy (GCMS) data.

Transformation of polyvinyl chloride (PVC) into a versatile and efficient adsorbent of Cu(II) cations and Cr(VI) anions through hydrothermal treatment and sulfonation

The reuse of waste polyvinyl chloride (PVC) has drawn much attention as it can reduce plastic waste and associated pollution, and provide valuable raw materials and products. In this study, sulfonated PVC-derived hydrochar (HS-PVC) was synthesized by two-stage hydrothermal treatment (HT) and sulfonation, and shown to be a versatile adsorbent. The removal of Cu(II) cations and Cr(VI) anions using HS-PVC reached 81.2 ± 1.6% and 60.3 ± 3.8%, respectively. The first stage of HT was crucial for the dichlorination of PVC and the formation of an aromatic structure. This stage guaranteed the introduction of -SO₃H onto PVC-derived hydrochar through subsequent sulfonation. HT intensities (i.e., temperature and time) and sulfonation intensity strongly determined the adsorption capacity of HS-PVC. Competitive adsorption between Cu(II) and Cr(VI) onto HS-PVC was demonstrated by binary and preloading adsorption. The proposed Cu(II) cations adsorption mechanism was electrostatic adsorption, while Cr(VI) were possibly complexed by the phenolic -OH and reduced to Cr(III) cations by CC groups in HS-PVC. In addition, HS-PVC derived from PVC waste pipes performed better than PVC powder for Cu(II) and Cr(VI) removal (＞90%). This study provides an efficient method for recycling waste PVC and production of efficient adsorbents.

Facile preparation protocol of magnetic mesoporous carbon acid catalysts via soft-template self-assembly method and their applications in conversion of xylose into furfural

Furfural is a valuable dehydration product of xylose. It has a broad spectrum of industrial applications. Various catalysts containing SO₃H have been reported for the conversion of xylose into furfural. Nevertheless, the multi-step preparation is tedious, and the catalysts are usually fine powders that are difficult to separate from the suspension. Novel magnetic mesoporous carbonaceous materials (Fe/MC) were successfully prepared via facile self-assembly in a single step. A facile subsequent hydrothermal sulfonation of Fe/MC with concentrated H₂SO₄ at 180°C gave mesoporous carbon bearing SO₃H groups (SO₃H@Fe/MC) without loss of the magnetic properties. Various techniques were employed to characterize the SO₃H@Fe/MC as a candidate catalyst. It showed strong magnetism due to its Fe particles and possessed a 243 m² g^-1 BET-specific surface area and a 90% mesopore volume. The sample contained 0.21 mmol g^-1 of SO₃H and gave a high conversion and an acceptable furfural yield and selectivity (100%, 45% and 45%, respectively) when used at 170°C for 1 h with γ-valerolactone as solvent. The catalyst was easily separated after the catalytic tests by using a magnet, confirming sufficient magneticstability. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 2)'.

Glucose isomerization catalyzed by swollen cellulose derived aluminum-hydrochar

Since efficient isomerization of glucose to fructose is vital for valorizing cellulose fraction of biomass to value-added chemicals, an approach of engineering aluminum-hydrochar catalyst by impregnating aluminum on swollen cellulose derived hydrochar has been studied. The results showed that Al-hydrochar calcinated at 300°C achieved fructose yield of 26.3% in acetone/H₂O reaction medium. It was found that the amorphous Al structures with nano-size on the surface of the carbon microspheres were the major contributor of the catalytic activity on glucose to fructose isomerization, while the formation of Al crystal had an inhibition effect on glucose isomerization. The deactivation study of Al-hydrochar catalysts showed the exfoliation of colloidal carbon containing aluminum active catalytic sites. This finding provides a novel strategy for efficient isomerization of glucose by Al-hydrochar prepared through hydrothermal carbonization and mild calcination activation process.

Rational design of solid-acid catalysts for cellulose hydrolysis using colloidal theory

Solid-acid catalysts functionalized with catalytic groups have attracted intense interest for converting cellulose into soluble products. However, design of solid-7 acid catalysts has been guided by molecular level interactions and the actual mechanism of cellulose-solid-acid catalyst particles adsorption remains unknown. Here, colloidal stability theory, DLVO, is used to rationalize the design of solid acids for targeted cellulose adsorption. In nearly all cases, an energy barrier, arising from electrostatic repulsion and much larger than the energy associated with thermal fluctuations, prevents close contact between the solid acid and cellulose. Polymer-based solid-acid substrates such as polystyrene and Nafion are especially ineffective as their interaction with cellulose is dominated by the repulsive electrostatic force. Carbon and metal oxides have potential to be effective for cellulose-solid-acid interaction as their attractive van der Waals interaction can offset the repulsive electrostatic interaction. The effects of reactor temperature and shear force were evaluated, with the finding that reactor temperature can minimize the catalyst-cellulose interaction barrier, promoting coagulation, but that the shear force in a typical laboratory reactor cannot. We have evaluated strategies for enhancing cellulose-catalyst interaction and conclude that raising reaction temperature or synthesizing acid/base bifunctional catalysts can effectively diminish electrostatic repulsion and promote cellulose-catalyst coagulation. The analysis presented here establishes a rational method for designing solid acid catalysts for cellulose hydrolysis.

Hydrolysis of Oligosaccharides and Polysaccharides on Sulfonated Solid Acid Catalysts: Relations between Adsorption Properties and Catalytic Activities

Sulfonated solid acid materials, such as sulfonated carbon catalysts, are promising materials as heterogeneous catalysts for the hydrolysis of esters and polysaccharides in water solvents. The catalytic active site is a sulfonic acid functional group. Compared to conventional strong acidic ion-exchange resin catalysts, sulfonated carbon materials have less sulfonic acid functional groups but higher catalytic activity for hydrolysis of polysaccharides per catalyst weight. However, the details of catalytic properties and the substrate suitability of both catalysts are unclear. In this study, the hydrolytic activities and the adsorption properties of both catalysts were investigated for various oligosaccharides and polysaccharides with varying degrees of polymerization (DP). The catalytic activities for the hydrolysis with increase of the DP of saccharides were found to increase over the sulfonated carbon catalyst but decrease over strong acidic ion-exchange resin catalyst. The inverse catalytic properties attribute to the dependence of the amounts of adsorption and/or penetration of saccharides on the DP. Moreover, the catalytic activity per acidic sites of strong acidic ion-exchange resin is in good agreement with the value obtained by multiplying the catalytic activity of a dilute sulfuric acid by the penetration degrees.

Conversion of biochar to sulfonated solid acid catalysts for spiramycin hydrolysis: Insights into the sulfonation process

Biochar has been recognized as a sustainable platform for developing functional materials including catalysts. This work demonstrated a method of converting biochar to sulfonated solid-acid catalysts, and the effectiveness of the catalysts for spiramycin hydrolysis was examined. Two biochar samples (H and X) were sulfonated with three reagents (concentrated H₂SO₄, ClSO₃H and p-toluenesulfonic acid (TsOH)) under hydrothermal, simple heating, ambient temperature, and CHCl₃-assisted treatments. The effect of elemental compositions and structural characteristics of the feeding materials (H and X) on the acidic properties of the sulfonated biochars were investigated. The results showed that the sulfonation ability of the three reagents was in the order of ClSO₃H > H₂SO₄ > TsOH, while hydrothermal treatment provided the highest total acidity, and largest amount of acidic groups (e.g., SO₃H, COOH and Ar-OH). Biochar X with higher O/C and N contents, and less graphitic features showed superior acidic properties than biochar H under all the employed treatments. The hydrolytic efficiencies of the sulfonated biochars under 200 W of microwave irradiation increased with increasing total acidity, and the amount of SO₃H and COOH groups. After sulfonation, the O/C of biochars increased, while H/C decreased, and the aromatic and graphitic features did not change. The electromagnetic energy absorbed by the sulfonated biochars did not notably contribute to spiramycin hydrolysis. Thus, this work demonstrated an effective and promising method for maneuvering biochar-based functional solid-acid catalysts for antibiotic remediation in contaminated water.

Investigation of heterogeneous sulfonated graphene oxide to hydrolyze cellulose and produce dark fermentative biohydrogen using Enterobacter aerogenes

The main aim of this work was investigating the potential of sulfonated graphene oxide (sGO) for hydrolysis of cellulosic substrates and dark fermentative hydrogen production from obtained hydrolysates using E. aerogenes. Sulfonation of graphene oxide was performed using chlorosulfonic acid which showed a high acid density of 4.63 mmol/g. Influence of the reaction time (1-5 h), temperature (90-180 °C) and sGO dosage (62.5-500 mg in 25 mL reaction volume) on the hydrolysis of pretreated microcrystalline cellulose was experimented. It revealed that the yield of glucose and total reducing sugars and selectivity can reach 454.4 ± 22.20 mg/g, 682.6 ± 30.67 mg/g and 95.5%, respectively, at 150 °C for 3 h using 250 mg sGO. The maximum hydrogen efficiency of 150.0 ± 5.65 mL/g was achieved under optimized conditions, which was 2.2-fold higher than that from the pretreated MCC substrate as control in the absence of sGO (67.3 ± 8.84 mL/g).

Comparison of hydrochar- and pyrochar-based solid acid catalysts from cornstalk: Physiochemical properties, catalytic activity and deactivation behavior

Biochar made from biowaste provides renewable carbon precursors for catalysts preparation. Here, solid acid catalysts were prepared through functionalizing biochars produced via hydrothermal and pyrolytic carbonization of cornstalk with -SO₃H groups. Hydrochar-based catalysts (HAC) and pyrochar-based catalysts (PAC) exhibited significantly different physiochemical properties, catalytic activities and deactivation behaviors. The test of catalytic effects on cellulose degradation uncovered that HAC had a higher density of -SO₃H but lower surface special area than PAC. Specifically, PAC prepared at 400 °C resulted in the maximum increase of cellulose conversion by 16.00-50.50%. In comparison, the highest yields of glucose (11.14%) and 5-hydroxymethylfurfural (29.54%) were achieved catalyzed via HAC prepared at 240 °C. The results of catalyst deactivation behavior further revealed that used catalysts had an obvious reduction of -SO₃H density. Interestingly, used HAC-240 catalysts showed similar patterns of weight loss to fresh ones due to its high stability.

Enhanced hydrolysis of cellulose by catalytic polyethersulfone membranes with straight-through catalytic channels

The aim of this study was to prepare sulfonated graphene oxide/polyether sulfone (GO-SO₃H/PES) mixed matrix membranes (GPMMMs) with high porosity and straight-through catalytic channels by segregation and used for dynamic and continuous hydrolysis of cellulose. The high porosity and segregation increased the exposure of catalysts synergistically and the formative GO-SO₃H enriched, straight-through catalytic channels had higher catalytic performance, enhancing the diffusion of hydrolytic products. Dynamic hydrolysis of cellulose is more efficient than static hydrolysis due to the enhanced contact between cellulose and catalysts achieved by the extra driving forces, and the further degradation of produced saccharides was suppressed due to the high freedom of products. The TRS reached 98.18% after 1 h at 150 °C with a catalyst/cellulose mass ratio of 1:5. More importantly, the immobilization of GO-SO₃H by PES improved its stability and reusability at high reaction temperature. This strategy provides guidance to the design of high-performance catalytic membranes.

Eco-Friendly Ca-Montmorillonite Grafted by Non-Acidic Ionic Liquid Used as A Solid Acid Catalyst in Cellulose Hydrolysis to Reducing Sugars

An effective and friendly method was developed for the production of reducing sugars (RS) from the hydrolysis of cellulose over the solid catalyst of Ca-montmorillonite (Mt) grafted by non-acidic ionic liquid (Mt-IL) in water. The effect of mass ratio, water dosage, reaction temperature, and time were investigated in a batch reactor. Raw Mt showed only a 7.9% total reducing sugars (TRS) yield for the catalytic hydrolysis of cellulose in water. As the Mt was grafted by -SO₃H and IL, the TRS yield greatly increased under the same reaction conditions. The highest TRS yield of 35.7% was obtained on the catalyst of Mt grafted by non-acidic IL at 200 °C with the mass ratio of catalyst to cellulose of 0.2 for 120 min. The high TRS yield for Mt-IL should be attributed to the synergistic effect of the dissolution of cellulose by IL and the exposed metal ions on the layer with water. Although the yield of TRS on Mt-IL decreased gradually with recycling runs, the decrease after the first run was not very serious compared to the fresh catalyst. This work provides a promising strategy for efficient cellulose hydrolysis into fine chemicals by Mt with non-acidic IL.