Adsorption of chromium(III) on lignin

Adsorption of Cu(ii) ions in aqueous solution by aminated lignin from enzymatic hydrolysis residues

Aminated lignin (AL) has been prepared by a Mannich reaction for the removal of Cu(ii) ions from aqueous solution.

Adsorption and mechanism of cellulase enzymes onto lignin isolated from corn stover pretreated with liquid hot water

BACKGROUND

In the bioconversion of lignocellulosic substrates, the adsorption behavior of cellulase onto lignin has a negative effect on enzymatic hydrolysis of cellulose, decreasing glucose production during enzymatic hydrolysis, thus decreasing the yield of fermentation and the production of useful products. Understanding the interaction between lignin and cellulase is necessary to optimize the components of cellulase mixture, genetically engineer high-efficiency cellulase, and reduce cost of bioconversion. Most lignin is not removed during liquid hot water (LHW) pretreatment, and the characteristics of lignin in solid substrate are also changed. To understand the interactions between cellulase and lignin, this study investigated the change in the characteristics of lignin obtained from corn stover, as well as the behavior of cellulase adsorption onto lignin, under various severities of LHW pretreatment.

RESULTS

LHW pretreatment removed most hemicellulose and some lignin in corn stover, as well as improved enzymatic digestibility of corn stover. After LHW pretreatment, the molecular weight of lignin obviously increased, whereas its polydispersity decreased and became more negative. The hydrophobicity and functional groups in lignin also changed. Adsorption of cellulase from Penicillium oxalicum onto lignin isolated from corn stover was enhanced after LHW pretreatment, and increased under increasing pretreatment severity. Different adsorption behaviors were observed in different lignin samples and components of cellulase mixtures, even in different cellobiohydrolases (CBHs), endo-beta-1, 4-glucanases (EGs). The greatest reduction in enzyme activity caused by lignin was observed in CBH, followed by that in xylanase and then in EG and β-Glucosidase (BGL). The adsorption behavior exerted different effects on subsequent enzymatic hydrolysis of various biomass substrates. Hydrophobic and electrostatic interactions may be important factors affecting different adsorption behaviors between lignin and cellulase.

CONCLUSIONS

LHW pretreatment changed the characteristics of the remaining lignin in corn stover, thus affected the adsorption behavior of lignin toward cellulase. For different protein components in cellulase solution from P. oxalicum, electrostatic action was a main factor influencing the adsorption of EG and xylanase onto lignin in corn stover, while hydrophobicity affected the adsorption of CBH and BGL onto lignin.

Optimization of process parameters for heavy metals biosorption onto mustard waste biomass

Mustard waste biomass was tested as a biosorbent for the removal of Pb(II), Zn(II) and Cd(II) from aqueous solution. This strategy may be a sustainable option for the utilization of such wastes. The influence of the most important operating parameters of the biosorption process was analyzed in batch experiments, and optimal conditions were found to include initial solution pH 5.5, 5.0 g biosorbent/L, 2 hours of contact time and high temperature. Kinetics analyses show that the maximum of biosorption was quickly reached and could be described by a pseudo-second order kinetic model. The equilibrium data were well fitted by the Langmuir model, and the highest values of maximum biosorption capacity were obtained with Pb(II), followed by Zn(II) and Cd(II). The thermodynamic parameters of the biosorption process (ΔG, ΔH and ΔS) were also evaluated from isotherms. The results of this study suggest that mustard waste biomass can be used for the removal of heavy metals from aqueous media.

Study of chromium(vi) removal from aqueous solution using nitrogen-enriched activated carbon based bamboo processing residues

Nitrogen functional groups were introduced by urea and melamine onto the surface of two bamboo processing residues derived activated carbons (ACs) and Cr(vi) adsorption was investigated by changing various parameters.

Adsorption performance of low-cost gelatin–montmorillonite nanocomposite for Cr(iii) ions

Preparation of gelatin–montmorillonite (G–MMT) nanocomposite from Na–montmorillonite (Na–MMT) and gelatin through intercalation method and its adsorption of Cr(iii).

Glow discharge electrolysis plasma induced synthesis of cellulose-based ionic hydrogels and their multiple response behaviors

The cellulose-based hydrogel which was prepared through glow discharge electrolysis plasma showed excellent swelling performance and multiple response behaviors.

Sorption of polycyclic aromatic hydrocarbons (PAHs) to lignin: effects of hydrophobicity and temperature

The study of the sorption of contaminants to lignin is significant for understanding the migration of contaminants in the environment as well as developing low cost sorbent. In this study, sorption of three polycyclic aromatic hydrocarbons (PAHs), naphthalene, acenaphthene and phenanthrene, to lignin was investigated. Sorption isotherms were well described by both linear and Freundlich sorption models. Sorption coefficients of PAHs to lignin from water obtained from regression of both linear model (K d) and Freundlich model (K f) were highly positively correlated with hydrophobicity of PAHs. The amorphous structure of lignin provided sufficient sorption domain for partitioning of PAHs, and the attraction between PAHs molecules and aromatic fractions in lignin via π-π electron-donor-acceptor (π-π EDA) interaction is hypothesized to provide a strong sorption force. Thermodynamic modeling revealed that sorption of PAHs to lignin was a spontaneous and exothermic process.

Insight into the roles of microbial extracellular polymer substances in metal biosorption

Biosorption presents a potent technology to remediate metal-contaminated aqueous environment or even to recover precious metals. Extracellular polymeric substances (EPS) are believed to play an important role in metal biosorption by microorganisms, but the reported results have been rather contradictory and the underlying mechanisms remain largely unclear so far. This review aims to clarify why large discrepancies existed for different EPS-metal systems through systematically exploring into the adsorption mechanisms and influential factors, and to offer some implications for advancing the implementation of metal biosorption technologies. The state-of-the-art methodologies for characterizing metal-EPS binding are summarized; several interaction mechanisms, including ion exchange, complexation and surface precipitation, are analyzed; the major influential factors such as EPS composition, metal species, solution chemistry and operating conditions are discussed; and lastly future research needs to advance the investigations and implementations of such biosorption processes are proposed.

Dispersive evaluation and surface chemistry of advanced, multifunctional silica/lignin hybrid biomaterials

Advanced silica/lignin hybrid biomaterials were obtained using hydrated or fumed silicas (Aerosil®200) and Kraft lignin as precursors, which is a cheap and biodegradable natural polymer. To extend the possible range of applications, the silicas were first modified with N-2-(aminoethyl)-3-aminopropyltrimethoxsysilane, and then with Kraft lignin, which had been oxidized with sodium periodate. The SiO2/lignin hybrids and precursors were characterised by means of determination of their physicochemical and dispersive-morphological properties. The effectiveness of silica binding to lignin was verified by FT-IR spectroscopy. The zeta potential value provides relevant information regarding interactions between colloid particles. Measurement of the zeta potential values enabled an indirect assessment of stability for the studied hybrid systems. Determination of zeta potential and density of surface charge also permitted the quantitative analysis of changes in surface charge, and indirectly confirmed the effectiveness of the proposed method for synthesis of SiO2/lignin hybrid materials. A particularly attractive feature for practical use is their stability, especially electrokinetic stability. It is expected that silica/lignin hybrids will find a wide range of applications (polymer fillers, biosorbents, electrochemical sensors), as they combine the unique properties of silica with the specific structural features of lignin. This makes these hybrids biomaterials advanced and multifunctional.

Fabrication, characterization and application of nitrogen-containing carbon nanospheres obtained by pyrolysis of lignosulfonate/poly(2-ethylaniline)

Lignosulfonate/poly(2-ethylaniline) (LS-PEA) composite nanospheres were prepared via in situ polymerization of 2-ethylaniline (EA) with lignosulfonate (LS) as a dispersant. LS-PEA nanospheres with an average diameter of 155 nm were obtained at an optimal LS concentration of 20 wt.%. Subsequently, nitrogen-containing carbon nanospheres were fabricated via direct pyrolysis of the LS-PEA composite nanospheres at 600-800 °C. The carbon nanospheres prepared by pyrolysis were used as anodes of lithium-ion batteries. The first charge and discharge capacity of carbon nanospheres prepared at 700 °C at current densities of 60 and 100 mA g(-1) were 980 and 432 mAh g(-1), and 764 and 342 mAh g(-1), respectively. The batteries still owned a high capacity of 353 and 296 mAh g(-1) after 20 cycles. The results indicated that these nitrogen-containing carbon nanospheres could be used as a promising candidate for electrode materials of lithium-ion batteries.

Chitosan/anionic surfactant microparticles synthesized by high pressure spraying method for removal of phenolic pollutants

Biopolymeric microparticles were prepared by rapid expansion of high pressure CO2-chitosan (Chi) solution in sodium bis-(2-ethyl hexyl) sulfosuccinate (AOT) solution. At pressures higher than 2 MPa, ultrafine particles were formed while under this value, wires were obtained. The formation of Chi/AOT complex was confirmed by Fourier Transform Infrared (FTIR) Spectroscopy, whereas scanning electron microscopy was used to characterize the morphology, size and shape of the particles. The FTIR spectrum proved the interaction between the sulfonate groups of AOT and the amino groups of Chi. Microparticles are quasi-spherical in wet conditions and irregular after freeze drying, presenting a rough surface with many pores. Lyophilized hydrophobic microparticles were used to remove phenol and o-cresol from aqueous solution, and the adsorption process showed a maximum efficiency in the 7–8 pH range. The uptake of phenol and o-cresol increased with the amount of particles and decreased with increasing the pollutant concentration. The adsorption occurred rapidly in the first 60–120 minutes, and leveled off thereafter.

Investigation of trace metal binding properties of lignin by diffusive gradients in thin films

The binding behavior of lignin for Pb, Cu, Co, Mn, Cd and Ni was studied using the diffusive gradients in thin films technique (DGT). Samplers with different structures of diffusive gel were used in the well-stirred systems containing known concentrations of metals along with (a) 10, 20 and 40 μM lignin and; (b) 0.64 and 6.47 μM Suwannee river fulvic acid+40 μM lignin at an ionic strength of 0.01 M (NaNO(3)) and pH=7. Diffusion coefficients of lignin complexes in acrylamide gels were estimated and found to be less than 5% of the equivalent coefficients for the uncomplexed metal ions. These values were used to calculate concentrations of labile metals from DGT measurements in solutions, where lignin could discriminate metals in the order of Pb(+2)>Cu(+2)>Cd(+2)>Ni(+2)>Co(+2)>Mn(+2). Stability constants (LogK) were calculated using Visual MINTEQ II and WHAM V software. The K values were compared with the stability constants from titration of Pb and Cd with 10 μM lignin aqueous samples and with those of humic substances in natural waters. The constants obtained from measurement of complexing capacities might bias the real corresponding values unless two line regression analyses on titration data are considered. The DGT study of fractionation of metal species at varying ratios indicated that the proportion of organic complexes decreased with increasing ratios and gradually more metals were exchanged with inorganic phases. Speciation of Pb and Cd is affected by the concentrations of FA, Cd is dominantly bound with FA while Pb is evenly partitioned between the ligands. The comprehensive knowledge of metal-lignin complexes sheds some light on in situ operational speciation information that can be achieved by DGT.

Adsorption of Cd(II) and Pb(II) from Wastewater onto Porous Lignin Beads

In this paper, a crosslinked porous lignin beads (PLB) as adsorbent was adopted to adsorb toxic Pb2+ and Cd2+ ions from aqueous solutions. The pore structure and surface morphology of PLB were characterized by by a variety of techniques. The influences of pH, contact time, initial metal ions concentration, temperatures were investigated. The results showed that the adsorption of both heavy metal ions increases with pH. The adsorption equilibrium data under different temperature can be successfully described by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Langmuir adsorption model showed the best fit to the adsorption data of Cd2+ and D-R model fits best to the adsorption data of Pb2+. The results obtained also indicated that the adsorption of Cd2+ and Pb2+ increased with increasing temperature indicating endothermic nature of the adsorption process. The kinetic study showed that Cd2+ adsorption followed pseudo-second order rate kinetics and Pb2+ adsorption followed pseudo-first order rate kinetics. Cd2+ adsorption on PLB was mainly through the chemisorption mechanism (ED-R between 12.62 kJ•mol-1 and 16.20 kJ•mol-1) while physical and chemical absorption coexistence was observed to Pb2+ adsorption. Desorption studies revealed that the desorption rate increased with increasing hydrochloric acid concentration and could finally reach 94 % and 85.1 % for Cd2+ and Pb2+, respectively, by adding 3 mol/L of HCl.

Highly effective adsorption of heavy metal ions from aqueous solutions by macroporous xylan-rich hemicelluloses-based hydrogel

Xylan-rich hemicelluloses-based hydrogel was developed as a novel porous bioadsorbent by graft co-polymerization of acrylic acid (AA) and xylan-rich hemicelluloses for adsorption of heavy metal ions (Pd(2+), Cd(2+), and Zn(2+)) from aqueous solutions. The chemical structure, the interaction between the hydrogel and metal ions, and the porous structure of xylan-rich hemicelluloses-g-AA hydrogel were revealed by Fourier transform infrared spectroscopy and scanning electron microscopy. The effects of AA and cross-linker dosage, pH value, contacting time, and initial concentration of metal ion on the adsorption capacity were studied. The adsorption equilibrium time was about 60 min from the adsorption kinetics study. The maximum adsorption capacities of Pd(2+), Cd(2+), and Zn(2+) were 859, 495, and 274 mg/g, respectively. Furthermore, xylan-rich hemicelluloses-g-AA hydrogel also exhibited highly efficient regeneration and metal ion recovery efficiency and can be reused without noticeable loss of adsorption capacity for Pd(2+), Cd(2+), and Zn(2+) after quite a number of repeated adsorption/desorption cycles.

Adsorption of mercury on lignin: combined surface complexation modeling and X-ray absorption spectroscopy studies

Adsorption of mercury (Hg) on lignin was studied at a range of pH values using a combination of batch adsorption experiments, a surface complexation model (SCM) and synchrotron X-ray absorption spectroscopy (XAS). Surface complexation modeling indicates that three types of acid sites on lignin surfaces, namely aliphatic carboxylic-, aromatic carboxylic- and phenolic-type surface groups, contributed to Hg(II) adsorption. The bond distance and coordination number of Hg(II) adsorption samples at pH 3.0, 4.0 and 5.5 were obtained from extended X-ray absorption fine structure (EXAFS) spectroscopy analysis. The results of SCM and XAS combined reveal that the predominant adsorption species of Hg(II) on lignin changes from HgCl(2)(0) to monodentate complex -C-O-HgCl and then bidentate complex -C-O-Hg-O-C- with increasing pH value from 2.0 to 6.0. The good agreement between SCM and XAS results provides new insight into understanding the mechanisms of Hg(II) adsorption on lignin.

Preparation and heavy metal ions biosorption of graft copolymers from enzymatic hydrolysis lignin and amino acids

Novel biosorbents, graft copolymers, were prepared via Mannich reaction from enzymatic hydrolysis lignin with glycine and cystine, respectively. The element content, FT-IR and fluorescence spectra, relative viscosity, and particle size of the copolymers were systematically investigated. Furthermore, effects of initial pH, ionic strength, temperature, contact time and initial metal ion concentration on the biosorption capacities of Cu(II) and Co(II) ions onto the copolymers were studied using batch sorption technique. It was found that the copolymers exhibited excellent biosorption characteristics for Cu(II) and Co(II) ions. The sorption kinetic data can be described well with a pseudo-second-order model, and the equilibrium data can be fitted well to the Langmuir and Freundlich isotherm for Cu(II) and Co(II) biosorption process, respectively. Surface complexation and ion-exchange modeling were performed to elucidate the biosorption mechanism involved because surfaces of the copolymers contained three main types of acid/base sites from the amino acid grafted copolymer units.

Facile preparation of hierarchical polyaniline-lignin composite with a reactive silver-ion adsorbability

A hierarchical polyaniline-lignin (PANI-EHL) composite was facilely prepared from aniline and enzymatic hydrolysis lignin in an aqueous solution of ammonia. The morphology, FTIR, UV-vis spectra, thermogravimetric analysis, and wide-angle X-ray diffraction analyses of the composite were systematically investigated. Furthermore, the sorption property of the PANI-EHL composite for silver ions in aqueous solution was studied via a static sorption technique. The result demonstrated that the PANI-EHL composite possessed a strongly reactive sorption characteristic for silver ions. Serrated silver threads with length up to 10 mm were obtained by using the PANI-EHL composite as a low-cost adsorbent. Moreover, the role of EHL and polyaniline in the PANI-EHL composite for silver ions sorption was investigated. The investigation indicated that the EHL unit could play a vital role in the chelation of silver ions, whereas the polyaniline unit played a leading role in redox sorption.

Industrial wastes as low-cost potential adsorbents for the treatment of wastewater laden with heavy metals

Industrial wastes, such as, fly ash, blast furnace slag and sludge, black liquor lignin, red mud, and waste slurry, etc. are currently being investigated as potential adsorbents for the removal of the heavy metals from wastewater. It was found that modified industrial wastes showed higher adsorption capacity. The application of low-cost adsorbents obtained from the industrial wastes as a replacement for costly conventional methods of removing heavy metal ions from wastewater has been reviewed. The adsorption mechanism, influencing factors, favorable conditions, and competitive ions etc. on the adsorption of heavy metals have also been discussed in this article. From the review, it is evident that certain industrial waste materials have demonstrated high removal capacities for the heavy metals laden with wastewater. However, it is to be mentioned that adsorption capacities of the adsorbents vary depending on the characteristics of the adsorbents, the extent of chemical modification and the concentration of adsorbates. There are also few issues and drawbacks on the utilization of industrial wastes as low-cost adsorbents that have been addressed. In order to find out the practical utilization of industrial waste as low-cost adsorbents on the commercial scale, more research should be conducted in this direction.

Adsorption of fluoride from aqueous solution by graphene

A batch adsorption system was applied to investigate the adsorption of fluoride from aqueous solution by graphene. The adsorption capacities and rates of fluoride onto graphene at different initial pH, contact time, and temperature were evaluated. The experimental results showed that graphene is an excellent fluoride adsorbent with an adsorption capacity of up to 17.65 mg/g at initial fluoride concentration of 25 mg/L and temperature of 298 K. The isotherm analysis indicated that the adsorption data can be well described by Langmuir isotherm model. Thermodynamic studies revealed that the adsorption reaction was a spontaneous and endothermic process.