Unveiling the mechanistic aspects of methylene blue adsorption onto a novel phosphate-decorated coconut fiber lignin

The aim of this work was to evaluate the adsorptive performance of the phosphorylated coconut fiber lignin (PCFL) obtained through an innovative biorefinery process for removing methylene blue (MB). PCFL was obtained using coconut fiber mixed with 85 % wt. H3PO4 at 70 °C for 1 h. Milled wood lignin (MWL) and PCFL were characterized by FTIR, CP-MAS 31P NMR, phosphorous and hydroxyl contents, pHPZC, and BET analyses. The batch adsorption tests evaluated the effects of the biosorbent (0.25 - 4 g L-1) and adsorbate dosages (2.5 - 7.5 mg L-1), contact time (0 - 60 min), pH (4 - 8), ionic strength (0.001 - 0.1 mol L-1) and temperature (298.15 - 318.15 K) on MB adsorption. Kinetic, equilibrium, and thermodynamic modeling were used. The phosphorous content on PCFL was 2.5 times higher than that of MWL. PCFL presented an enhanced adsorptive performance for removing MB, which was spontaneous (ΔG0 < 0), endothermic (ΔH0 > 0), with affinity between the biosorbent and adsorbate (ΔS0 > 0), and driven by physisorption (Ea > 40 kJ mol-1). The adsorptive performance of PCFL was enhanced due to the grafting of new active sites by using an innovative biorefinery process, showing its potential to be used for textile effluent remediation.

High-performance acetosolv lignin-incorporated DGEBA cured with aprotic imidazolium-based ionic liquid: Polymerization, chemical, thermal and combustion aspects of the thermosetting materials

The lignin valorization constitutes a chemical platform for several segments of chemical industry. The aim of this work was to evaluate the potential of acetosolv coconut fiber lignin (ACFL) as an additive to DGEBA, curing it using an aprotic IL ([BMIM][PF₆]) and analyze the properties of the obtained thermosetting materials. ACFL was obtained by mixing coconut fiber with 90 % acetic acid and 2 % HCl at 110 °C during 1 h. ACFL was characterized by FTIR, TGA and ¹H NMR. The formulations were fabricated by mixing DGEBA and ACFL at different concentrations (0-50 % wt.). The curing parameters and [BMIM][PF₆] concentrations were optimized by DSC analyses. The cured ACFL-incorporated epoxy resins were characterized by gel content (GC), TGA, MCC and chemical resistance in different media. ACFL undergone a selective partial acetylation that favored its miscibility with DGEBA. High GC values were obtained at high curing temperatures and ACFL concentration. The crescent ACFL concentration did not affect the T_onset of the thermosetting materials significantly. ACFL has increased the resistance of DGEBA to combustion and different chemical media. ACFL has shown a great potential to be used as a bio-additive for enhancing the chemical, thermal and combustion properties of high-performance materials.

Development of a phosphorous-based biorefinery process for producing lignocellulosic functional materials from coconut wastes

This work aimed to develop a phosphorous-based biorefinery process for obtaining phosphorylated lignocellulosic fractions in a one-pot protocol from coconut fiber. Natural coconut fiber (NCF) was mixed with 85 % m/m H₃PO₄ at 70 °C for 1 h to yield the modified coconut fiber (MCF), aqueous phase (AP), and coconut fiber lignin (CFL). MCF was characterized by its TAPPI, FTIR, SEM, EDX, TGA, WCA, and P content. AP was characterized regarding its pH, conductivity, glucose, furfural, HMF, total sugars and ASL contents. CFL structure was evaluated by FTIR, ¹H, ³¹P and ¹H-¹³C HSQC NMR, TGA and P content and was compared to that of milled wood lignin (MWL). It was observed that MCF and CFL were phosphorylated during the pulping (0.54 and 0.23 % wt., respectively), while AP has shown high sugar levels, low inhibitor content, and some remaining phosphorous. The phosphorylation of MCF and CFL also showed an enhancement of their thermal and thermo-oxidative properties. The results show that a platform of functional materials such as biosorbents, biofuels, flame retardants, and biocomposites can be created through an eco-friendly, simple, fast, and novel biorefinery process.

Elucidating the adsorption mechanism of Rhodamine B on mesoporous coconut coir-based biosorbents through a non-linear modeling and recycling approach

The search for renewable adsorbent materials has increased continuously, being the agro-wastes an interesting alternative. This work aimed to elucidate the mechanism of adsorption of Rhodamine B on crude and modified coconut fibers from aqueous systems and the feasibility of reusing the biosorbents. The chemical modification of crude coconut fiber was carried out by the organosolv process. The biosorbents were characterized by lignocellulosic composition, FTIR, TGA, WCA, SEM, nitrogen adsorption/desorption (BET-BJH), and pH of zero point of charge (pH_PZC) analyses_. The batch adsorption tests evaluated the effects of the adsorbent and adsorbate dosages, contact time, and temperature on Rhodamine B adsorption. For elucidating the adsorption mechanisms involved in the process, the non-linear forms of kinetic and isotherm models were used. The regeneration of the biosorbents was evaluated by carrying out the desorption experiments. Modified coconut fiber had an increase in the amount of α-cellulose, which influenced its structural, morphological, surface, and porous properties. The removal efficiency of Rhodamine B was about 90% for modified coconut fiber and 36% for crude coconut fiber. The dye adsorption was spontaneous and endothermic for both biosorbents, showing higher spontaneity and affinity with the adsorbate for biosorbent modified. Therefore, the coconut fiber can be considered an alternative to the traditional adsorbent materials that allows the reuse by four times without performance loss, in which its adsorptive capacity has increased through its chemical modification by a biorefinery process.

Unraveling the adsorption mechanism of methylene blue onto selective pH precipitated Kraft lignins: Kinetic, equilibrium and thermodynamic aspects

Lignin has been used on its crude or modified forms for adsorption purposes. This work evaluated the influence of selective pH precipitation of Kraft lignins (KLs) on their adsorptive performance for removing methylene blue (MB). The alkaline and acid KLs (KL A and KLB, respectively) were characterized by FTIR, ³¹P NMR, GPC and pH_PZC analyses. The effects of biosorbent and adsorbate concentrations, pH, ionic strength, contact time and temperature on the MB adsorption were evaluated. The equilibrium, kinetic and thermodynamic parameters were calculated by Langmuir and Freundlich isotherms, pseudo-first and second order and Van't Hoff and Gibbs models, respectively. KL A and KL B presented peculiar structural features, mainly hydroxyls concentration and M_w values, which have influenced on the removal efficiency of MB and the adsorptive capacities of KL A (>80 %; ≥80 mg g^-1) and KL B (>90 %; ≥20 mg g^-1), respectively. The equilibrium, kinetic and thermodynamic parameters have shown that MB adsorption presented different mechanisms for each KL, but it only has driven by chemisorption for KL B. Therefore, KL A and KL B can be considered as potential novel biosorbents obtained through a clean, fast and simple route for textile wastewater treatment.

Development of an eco-friendly acetosolv protocol for tuning the acetylation of coconut shell lignin: Structural, antioxidant, solubility and UV-blocking properties

The optimization of the parameters involved in lignin extraction is crucial for obtaining a lignin with specific structural features for its further valorization. The aim of this work was to develop an eco-friendly organosolv protocol for tuning the acetylation degree of coconut shell lignins (CSLs) by using MgCl₂ and HCl as catalyst and co-catalyst, respectively. CSLs were obtained by mixing coconut shell powder with 90% v/v acetic acid combined to no catalyst, 2% v/v HCl and 2% w/v MgCl₂ (1, 2 and 3 h) and 2% w/v MgCl₂ combined to 0.1, 0.25 and 0.5% v/v HCl (2 h) at 110 °C. CSLs were characterized by FTIR, ¹H NMR, GPC and TGA. The effects of the acetylation degree were evaluated on their antioxidant activity (DPPH assay) and UV-blocking capacity in sunscreen formulations. The results have shown that the use of HCl as co-catalyst increased the lignin yield (from 21.4 to 48.8%) and the acetylation degree (from 0.81 to 1.58 mmol g^-1), which positively affected thermal (200 < T_onset < 226 °C), antioxidant (46.6 < IC₅₀ < 67.5 μg mL^-1) and UV-blocking capacities of CSLs. It can be concluded that the design of the organosolv process was capable of generating lignins with peculiar functionalities and properties through an eco-friendly protocol.

Safety aspects of kraft lignin fractions: Discussions on the in chemico antioxidant activity and the induction of oxidative stress on a cell-based in vitro model

Lignin is a complex phenolic biopolymer present in plant cell walls and a by-product of the cellulose pulping industry. Lignin has functional properties, such as antioxidant activity, that make it a potential natural active ingredient for health-care products. However, not all safety aspects of lignin fractions have been adequately investigated. Herein, we evaluated the antioxidant and genotoxic potential of two hardwood kraft lignins (F3 and F5). The chemical characterization of F3 and F5 demonstrated their thermal stability and the presence of different phenolic units, while the DPPH assay confirmed the antioxidant activity of these lignin fractions. Despite being antioxidants in the DPPH assay, F3 and F5 were capable of generating intracellular reactive oxygen species (ROS) and subsequently causing oxidative DNA damage (Comet assay) in HepG2 cells. The biological relevance of the DPPH assay might be uncertain in some cases; therefore, we suggest combining in chemico tests with biological system-based tests to determine efficacy and safety levels of lignins and define appropriate applications of lignins for consumer products. Moreover, kraft lignins obtained by acid precipitation may pose risks to human health; however, as genotoxicity is not the sole endpoint of toxicity required in hazard assessments, additional toxicological evaluations are needed.

Improving cause of death certification in the Philippines: implementation of an electronic verbal autopsy decision support tool (SmartVA auto-analyse) to aid physician diagnoses of out-of-facility deaths

Background

The majority of deaths in the Philippines occur out-of-facility and require a medical certificate of cause of death by Municipal Health Officers (MHOs) for burial. MHOs lack a standardised certification process for out-of-facility deaths and when no medical records are available, certify a high proportion of ill-defined causes of death. We aimed to develop and introduce SmartVA Auto-Analyse, a verbal autopsy (VA) based electronic decision support tool in order to assist the MHOs in certifying out-of-facility deaths.

Method

We conducted a stakeholder consultation, process mapping and a pre-test to assess feasibility and acceptability of SmartVA Auto-Analyse. MHOs were first asked to conduct an open-ended interview from the family members of the deceased, and if they were not able to arrive at a diagnosis, continue the interview using the standardised SmartVA questionnaire. Auto-Analyse then presented the MHO with the three most likely causes of death. For the pilot, the intervention was scaled-up to 91 municipalities. We performed a mixed-methods evaluation using the cause of death data and group discussions with the MHOs.

Results

Of the 5649 deaths registered, Auto-Analyse was used to certify 4586 (81%). For the remaining 19%, doctors believed they could assign a cause of death based on the availability of medical records and the VA open narrative. When used, physicians used the Auto-Analyse diagnosis in 85% of cases to certify the cause of death. Only 13% of the deaths under the intervention had an undetermined cause of death. Group discussions identified two themes: Auto-Analyse standardized the certification of home deaths and assisted the MHOs to improve the quality of death certification.

Conclusion

Standardized VA combined with physician diagnosis using the SmartVA Auto-Analyse support tool was readily used by MHOs in the Philippines and can improve the quality of death certification of home deaths.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-10542-0.

Microwave-assisted selective acetylation of Kraft lignin: Acetic acid as a sustainable reactant for lignin valorization

Lignin acetylation, one of the most widespread chemical modifications used for improve the solubility of this biopolymer in organic solvents and increase polymer-lignin compatibility, has been performed for decades using time-consuming methodologies and acetylating agents with serious drawbacks. Moreover, traditional acetylation reactions generally conduce to non-selective acetylation of both aliphatic and phenolic groups. In this work, we demonstrated that partial and selective acetylation of kraft lignin can be carried out through a greener, simple and fast microwave-assisted process using acetic acid as solvent and acetylating agent. Structural characterization via FTIR, ¹H-¹³C HSQC and ³¹P NMR demonstrated that acetylation reaction occurs selectively only in aliphatic hydroxyls, preserving the phenolic hydroxyls. Optimal reaction conditions were obtained using 1% (v/v) of H₂SO₄ as catalyst and only 5 min as reaction time. The acetylated Kraft lignin (AKL) obtained, have enhanced solubility in organic solvents (ethyl acetate, chloroform and dichloromethane) compared to unmodified Kraft lignin (KL) and antioxidant capacity almost 8 times higher than a commercial antioxidant BHT. These characteristics make the partially and selectively acetylated Kraft lignin a potential green antioxidant additive to be used in polymers blends.