Carbon materials based on lignin and their environmentally friendly applications

Carbon materials based on lignin and their environmentally friendly applications | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Carbon materials based on lignin and their environmentally friendly applications mouna jaouadi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5034064/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The green revolution concept has accelerated the pace of innovation to avoid the use of materials that can harm the environment. In this work, the valorization of lignin and olive wastes was studied. Olive stone used to prepare activated carbons which are modified by lignin. The carbons were characterized by TGA-DTA, FTIR spectroscopy, adsorption-desorption of N 2 at 77K, Boehm titration and the measure of pH PZC . FTIR results show the presence of some groups that confirm that carbons based lignin can be used as fertilizers. BET results show micro- mesoporous structure of carbons materials, they might be used as electrodes. Boehm titration shows the increase of phenolic groups in modified carbon, which confirms that lignin can be used as bio-composites. The thermal analyses show the high stability after lignin coating so the carbon based on lignin can be used as a green biofuel. Lignin olive stone activated carbon valorization adsorption Figures Figure 1 Figure 2 Figure 3 1. Introduction Cellulose and hemicellulose, lignin is a highly abundant biopolymer. As a major component of lignocellulosic materials, lignin accounts for a significant proportion of biomass including wood and agricultural residues. It has great potential for utilization as a green raw material or as an additive in various industrial applications, it can be used as an adhesive or tanning agent and it is used for paper industry (Tong H et al .2019). According to literature, much of the lignin produced by the paper industry is consumed as a fuel and the annual production of industrial lignin in the world is more than 70 million tons (De Wild P.J et al.2012, Suhas, P.J.M et al.2007). Other applications such as production of activated carbons (ACs) and carbon fibers from lignin have also gained much interest in the last few years. Lignin has been proven to be a good source for producing activated carbons using chemical activation methods. In addition to that, lignin has been used as a precursor or feedstock for the preparation of high-performance electrochemical energy materials and components such as electrodes, electrolyte additives, membrane separators, and binders. Therefore, using waste biomass to produce activated carbons for water treatment is a potential method for comprehensive utilization of biomass waste. Olive stone is a waste, which is largely produced in the Mediterranean countries as Tunisia, where there are more than 60 million olive trees (Hannachi H et al.2007). Tunisia is the world’s second largest olive oil producer and during olive oil production process approximately 35–40 kg of olive pomace is released per 100 kg of olive, it represents roughly 10% by weight of olive ( Sellami F et al. 2008 ). The use of this solid waste as a precursor for the preparation of activated carbon produces not only a high-quality adsorbent with low inorganic content for the purification of contaminated environments, but also contributes to minimizing the environmental impact of solid wastes. Recently, the modification of carbonaceous materials seems particularly promising for improving the absorbents affinity. The literature review shows that the modifications of AC surface improve the properties by different treatment applications such as carbon dioxide adsorption (Shafeeyan MS et al. 2010 , Chiang Y-C et al.2017), removal of siloxanes from landfill gas ( Gong H et al. 2007 ) , removal of contaminants from aqueous solutions (Yin C.Y et al.2007, Suhas et al.2016 ) . In addition, the porous structure of activated carbon depends on the pore size: meso- and macropores allow the diffusion of charged species whereas micropores favor the accumulation of charged species so carbon materials prepared from olive stone can be used as electrodes ( Jaouadi M. 2020 ) . The main objective of this work was to develop a new method for olive waste and lignin management by preparing activated carbon which modified by coating silica and lignin. But to our knowledge, studies focusing on preparing and modification of activated carbon by lignin are few. The prepared composites could use as an adsorbent, fuel or for energy storage (used as an electrode). The thermal behavior, the structure, the porosity, and the general composition were studied using TGA-DTA, FTIR spectroscopy, adsorption-desorption of N 2 at 77K, Boehm titration and the measure of pH PZC . 2. Materials and methods 2.1 Synthesis of activated carbon and activated carbon coated by silica In our previous work, an activated carbon was prepared from olive stones and modified by silica ( Jaouadi, M., 2021 ) . The carbon materials are referred in the text as “AC’’ and “AC-Silica”. 2.2 Modification the prepared carbon materials by lignin 1 g of industrial lignin (Supplied by a nursery in Soliman-Tunisia, 33% of humic acid and 67% fulvic acid) was added to 1 g of AC and/ or AC-Silica, the mixture was stirred at 60°C during 12h. The composite AC-lignin was washed using distilled water. 2.3 Physico-chemical characterizations The pH PZC values were determined by a mass titration method proposed by M.V Lopez and al. ( Lopez-Ramon, M.V et al. 1999). Various amounts of carbon materials were put in 10mL of 0.1mol L − 1 NaCl solutions (prepared with boiled water). The bottles were sealed and shaken in a thermostat shaker overnight, the equilibrium pH values of the mixtures were measured, and the limiting pH was taken as the pH PZC . The functional (acidic) groups present on the surface were quantified by Boehm ‘s titration ( Strelko V et al.2002 ). Experimentally, 0.1 g of carbon materials powder was mixed with 20 mL of 0.02 mol.L − 1 aqueous solutions composed by either NaOH, Na 2 CO 3 or NaHCO 3 reactants. The mixtures were stirred for 48 h at a constant speed of 150 rpm at room temperature. Then, the suspensions were filtered through 0.45 µm membrane filters (Millipore 405314). To determine the contents of oxygenated groups, back-titrations of the filtrate (10 mL) were performed with standardized HCl (0.02 mol. L − 1 ). The numbers of acidic sites were calculated by assuming that NaOH neutralizes the carboxyl, phenolic and lactonic groups, while Na 2 CO 3 neutralizes the carboxyl and lactonic groups, and NaHCO 3 neutralizes the carboxyl groups only. The characterization of prepared AC and AC-Si powders by Fourier transforms infrared (FT-IR) spectroscopy were performed using a Spectrum 100 FTIR spectrometer (PerkinElmer- France). The transmission spectra were recorded using KBr pellets. All spectra were obtained in the 4000 − 400 cm − 1 range at a resolution of 4 cm − 1 . The thermal analyses (TGA-DTA) of carboneous materials were carried out with a SETARAM apparatus. Experiments were performed under an argon gas at a heating rate of 5°C min − 1 in the temperature range of 25-1100°C by using 17.5 mg of each sample. The specific surface areas and pore size distributions were obtained from the adsorption/desorption isotherms of N 2 at 77 K using an automatic sorptometer (ASAP 2020, Micromeritics, USA). Prior to each measurement, the sample was degassed during 48h at 250°C for AC and 100°C for AC-Si, AC-lignin and AC-Silica-lignin to avoid the decomposition of the surface groups. Then, specific surface areas of prepared powders were calculated from the Brunauer-Emmett-Teller (BET) equation. 3. Results and discussion 3.1. Characterization of the carbon materials 3.1.1. Boehm titrations and pH PZC The pH PZC value of AC (2.25) is in agreement with the one (i.e. 3.7) measured by Clark et al. (Clark, H.M. et al. 2012) for an activated carbon prepared by H 3 PO 4 activation of coffee residues at 350°C. The pH PZC of AC increased after silica coating (2.6). For such low values (pH PZC < 4.5, (Kosmulski M. 2002 ) , amphoteric silanol groups are deprotonated and the net surface charge is negative over a wide pH range. The low pH PZC values for all carbon materials are generally associated to the presence of acidic carboxylic functional groups. The pH PZC values were confirmed by the acidic character of activated carbons surface measured by Boehm titration‘s method. Table 1 indicates the amounts of carboxylic, phenolic, lactonic and acidic groups present on as-prepared carbonaceous surfaces. The AC-Silica and AC- Lignin-Silica surface present the highest amount of acidic groups. The increase in the content of oxygenated groups after the Si coating is mainly due to the formation of additional carboxylic groups. According to Jaouadi et al. ( Jaouadi, M et al. 2021 ) the increase of the content of oxygenated groups after the Si coating is mainly due to the formation of additional carboxylic groups that are beneficial for the hydrophilicity and wettability of carbonaceous surfaces, the AC-Silica and AC-lignin-Silica can be used as electrodes for electrochemical devices especially for supercapacitors. AC has a small quantity of phenolic groups, which confirms that after preparation of activated carbon from olive wastes (olive stone) the phenolic groups were removed. The study of Monetta et al. ( Monetta P et al. 2012 ) confirmed that olive wastes when applied, as a soil amendment produce a high increase in polyphenol levels, so preparing an activated carbon from olive stones will remove phenolic compounds. Table 1 pH PZC , total surface acid groups of the carbon materials (mmol/g : determined by Boehm titrations). pH PZC Carboxylic Phenolic Lactonic Acidic AC 2.25 0.06 0.07 0.06 0.19 AC-Silica 2.6 1.3 0.8 0.6 2.08 AC-Lignin 2.2 0.08 0.1 0.02 0.2 AC-Lignin-Silica 2.4 1.6 1 0.04 2.63 3.1.2. FTIR analyses FTIR spectra of AC, AC-Silica, AC-Lignin and AC-Lignin-Silica are shown in Fig. 1 . For all the samples, the stretching vibrations of -OH groups (υ OH ), observed around 3500 cm − 1 , are attributed to the adsorbed residual water on carbons and are related to the hydrogen bond formed by the association of O-H, and the peak at 3290 cm − 1 were verified to be the hydroxyl association belongs to carboxylic acid. For AC-Silica-Lignin and AC-Lignin the high intensity of this υ OH band could be related to the high amount of phenolic groups in this material. For both samples, the band at 1700 cm − 1 (υ C=O ) is assigned to the C = O stretching vibrations of ketones, aldehydes, lactones or carboxyl groups ( Strelko V. 2002 ) . The broad band at 1000–1300 cm − 1 (maxima at 1190–1200 cm − 1 ) has been assigned to C-O stretching in acids, alcohols, phenols, ethers and/or esters groups ( Jaouadi M et al.2021 ) . This band is particularly more intense for AC-Si. The strong C-O-C stretching bands (υ C−O−C ) were also observed from 1100 to 1200 cm − 1 for AC-Silica, indicating the presence of aromatic ether or ester bond. The presence of Si in AC-Si composites is confirmed by the weak band located at 955 cm − 1 , ascribed to Si-O-H asymmetry stretching and bending vibration, and bands at 1090 and 650 cm − 1 corresponding to Si-O-Si asymmetric and symmetric stretching, respectively ( Jaouadi, M et al. 2021 ). The peak at 1030 cm − 1 appeared in the AC-Silica-Lignin and AC-Lignin was ascribed to the C-OH and C–O-C stretching of the side groups and glycosidic bonds, respectively [18] . The intensity at 1461 cm –1 in both carbon materials modified by lignin was attributed to the methoxy C–H bending and C–C stretching in the aromatic skeleton ( Shi Z et al.2019 ) . It can be found that the characteristic peaks corresponding to lignin appeared in AC-Lignin and AC-Silica-Lignin, these phenomena confirmed the reaction between lignin and carbon materials. Lignin contains phenolic component and the presence of several functional groups (OH, COOH, and C = O), lignin has the potential to be valorized for bio-composites and antioxidant materials ( Umme M. A et al. 2021). These are useful in the agroindustry as additives, coating agents, adsorbents, plant growth stimulators for food production, packaging materials, and fertilizers ( Maurice N.C et al. 2020 ). Therefore, carbon materials modified by lignin probably play the same role of lignin. Another side, oxygen-containing functional groups found in carbon material surfaces play a vital role in the adsorption. Notably, the peaks of the -OH, -COOH groups displayed the adsorption of heavy metal ions due to the possible formation of complexes with them ( Zawadzki J.1989 ). 3.1.3. Porosity characterization Figure 2 shows the N 2 adsorption–desorption isotherms (at 77 K) of AC, AC-Silica, AC-Lignin and AC-Silica-Lignin. The isotherms of AC, AC-Silica exhibit an IV–type profile that reflects the existence of micro- and mesopores. The isotherms of AC-Lignin and AC-Silica-Lignin are type I and typical of mainly microporous activated carbons. In the AC-Lignin and AC-Silica-Lignin composites the volume has sharply decreased compared to AC and AC-Silica (Table 2 ). The BET specific surface area (Table 3) was decreased after lignin reaction with AC and AC-Silica (from 957.26 to 642.5 and from 902 to 375. 12 m 2 .g − 1 , respectively) because the pores were either collapsed or blocked after strong reaction with lignin. The AC-Silica-Lignin composite showed a low specific surface, which indicated that free pores of activated carbon were occupied by silica upon modification and pores of AC-Silica, was also covered by lignin upon reaction. Probably the component of lignocellulosic precursors found in lignin primarily responsible for the microporosity of activated carbons ( Suhas, P.J.M et al. 2007 ). According to Wang et al. (Wang X et al.2018) lignin has been considered as the substrate of adsorbents because of its low price and easy modification, most importantly, its ability to accelerate the adsorption rate of heavy metal ions (Wang X at al.2021). The prepared activated carbon can be used as adsorbents or as electrodes for energy storage. The mesoporous structure is expected to improve the electrochemical performance by enhancing the ionic mobility, while micropores are more efficient for the charge accumulation. In the same way, the wettability of the electrode may be affected by the size of electrolyte ions in regards to the pore size of the surface ( Chmiola J et al. 2006 ). Table 2 Porosity characteristics of AC, AC-Lignin, AC-Silica and AC-Silica-Lignin. Samples Surface area S BET (m 2 .g − 1 ) Pore volume V tot (cm³.g − 1 ) Micropore area (m 2 .g − 1 ) Mesopore area (m 2 .g − 1 ) External area (m 2 .g − 1 ) Micropore volume V m (cm³.g − 1 ) AC 957.26 0.59 601.36 355.64 355.89 0.27 AC-lignin 642.5 0.11 565.35 77.15 77.16 0.28 AC-Silica 902 0.57 550.27 351.73 351.83 0.25 AC-Silica-Lignin 375.12 0.24 304.99 70.13 70.13 0.15 AC-Silica, AC-Lignin and AC-Silica-Lignin. 3.1.4 TGA-DTA analyses The thermal stability of electrode materials is a significant parameter. Hence, TGA/TDA measurements were carried out for AC, AC-Silica, AC-Lignin and AC-Silica-Lignin powders as presented in Fig. 3 . The weight losses carbon materials are mainly embodied in the temperature range over 120°C and attributed to the decomposition of carbon frameworks ( Zawadzki J. 1989 ). The weight losses of AC, AC-Silica, AC-Lignin and AC-Silica-Lignin are established in three stages; when the temperature is below 150°C, the weight loss of ~ 20% is caused by the desorption of water. From 150 to 500°C, the loss is about ~ 10% and results from the decomposition of oxygenated functional groups. From 500 to 1100°C, the weight loss is about 13, 20, 20 and 14% for AC, AC-Silica, AC-Lignin and AC-Silica-Lignin, respectively. This weight loss corresponds to the decomposition of the organic compounds. It is noticed that DTA curves of AC, AC-Silica samples present very similar decomposition profiles. The endothermic transition at 120°C, due to water vaporization, is followed by an exothermal transition at 450°C. For AC-Lignin and AC-Lignin-Silica, the exothermal transition at 450° was disappeared after reaction with lignin. The DTA curves of carbon materials modified by lignin (AC-Lignin and AC-Lignin-Silica) analyzed in this work, shows an endothermic peak between 400 and 1000°C, which may be assigned to decarboxylation reactions ( Jaouadi M. 2020 ). Lignin has special features such as thermal stability and can be used a compost.Industrial lignin is currently not fully utilized. A large amount of industrial lignin is discarded as waste or burned only as a low-value fuel. In short, the addition of lignin in AC and in AC-Silica enhanced the overall thermal stability of the adsorbents, and confirmed that lignin was successfully grafted onto the carbon materials (AC and AC-Silica). On the other hand, carbon materials modified by lignin can be consumed as a fuel. The main advantage of coating of lignin into carbon surfaces is to reduce the high ash fractions and to increase the energetic density. Hence, Tunisia and other emerging countries, lacking sources of classic fossil fuels can base energy policy on economic and sustainable alternatives like agropellets. Several authors described the thermal degradation as a progressive decomposition of their cellulose, hemicelluloses and lignin ( Ouatmane A et al.2000). 4. Conclusion Olive wastes and lignin were key compounds and have a great importance for the development of sustainable biomass valorization and they were successfully developed. FTIR results show the presence of some active functional groups, which play a vital role in the adsorption and confirm that modified carbon by lignin, can be used as plant growth stimulators and fertilizers. Boehm titration shows the increase of phenolic groups in carbon based lignin, which confirms that lignin has the potential to be valorized for bio-composites and antioxidant materials. The thermal analyses show the high stability after lignin coating so the carbon based on lignin can be used as a green biofuel. Carbon based on lignin can be used as electrodes for energy storage. Declarations Funding This work was supported by research program of the Tunisian Ministry of Higher Education Conflicts of interest/ Competing interests The authors declare no competing interests Availability of data and materials All data generated and analyzed during the current study are included in this article Code availability Not applicable Author’s contributions Mouna Jaouadi: Material preparation, Materials characterization, original draft preparation, Reviewing and supervision. References Chiang Y-C, Juang RS (2017) Surface modifications of carbonaceous materials for carbon dioxide adsorption: a review. J Taiwan Inst Chem Eng 71:214–234 Chmiola J, Yushin G, Gogotsi Y, Simon P, Taberna PL (2006) Anomalous increase in carbon at pore sizes less than 1 nanometer. 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Bioresour Technol 98:2301–2312 Suhas GVK, Carrott PJM, Singh R, Chaudhary M, Kushwaha S (2016) Cellulose: a review as natural, modified and activated carbon adsorbent. Bioresour Technol 216:1066–1076 Tong H, Nanta S, Ayumu T, Olena S, Pelle M, Weihong Y (2019) Characterization of lignin at pre-pyrolysis temperature to investigate its melting problem. Fuel 235:1061–1069 Wang X, Jiang C, Hou B, Wang Y, Hao C, Wu J (2018) Carbon composite lignin-based adsorbents for the adsorption of dyes. Chemosphere 206:587–596 Wang X, Li X, Peng L, Han S, Hao C, Jiang C, Wang H, Fan X (2021) Effective removal of heavy metals from water using porous lignin-based adsorbents. Chemosphere 279:1305 Umme MA, Na J, Hanyang L, Qiong W, Chunfeng S, Qingling L Degang, M. Xuebin L (2021) Can lignin be transformed into agrochemicals? Recent advances in the agricultural applications of lignin. Ind Crops Prod 170:113646 Yin CY, Aroua MK, Daud WMAW (2007) Review of modifications of activated carbon for enhancing contaminant uptakes from aqueous solutions. Sep Purif Technol 52:403–415 Zawadzki J (1989) Infrared spectroscopy in surface chemistry of carbons. In: Thrower PA (ed) Chemistry and physics of carbon, vol 21. Marcel Dekker, New York, 1989 pp 147–3860 Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5034064","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":365001152,"identity":"a27dea5e-4922-4b07-8bf9-20155a3319a2","order_by":0,"name":"mouna jaouadi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAx0lEQVRIiWNgGAWjYBACNjiLvQFIGFiQooXnAEiLBCn2SSSAScIK+aTbLzDdqDicxz/z+dUNPwokGPjbuxPwO0zmTAFzzpnDxRK3c8pu9gAdJnHm7Ab8WiRyEphz2w4nNtzOSbvBA9RiIJFLpJb5N8+k3fxDnJb0A2AtG26wH7tNrC0Mh3POpCduPJPDdlvGQIKHoF/kZ6Q/fJxTYZ047/jxZzff/LGR42/vxa8FGIUGB2AMMElAOQiwP0BnjIJRMApGwShABQDwKEgA6BqaHgAAAABJRU5ErkJggg==","orcid":"","institution":"CNRSM: Centre National de Recherches en Sciences des Materiaux","correspondingAuthor":true,"prefix":"","firstName":"mouna","middleName":"","lastName":"jaouadi","suffix":""}],"badges":[],"createdAt":"2024-09-04 22:15:30","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5034064/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5034064/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":66640835,"identity":"a49e9cd5-4948-4760-ab8d-8a823323a811","added_by":"auto","created_at":"2024-10-15 06:07:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":21979,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectra of AC, AC-Silica, AC-Lignin and AC-Silica-Lignin.\u003c/p\u003e","description":"","filename":"Onlinefloatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5034064/v1/41742015baead847ffb241b6.png"},{"id":66640840,"identity":"67ca42fd-4466-45a7-aa2e-7d76b5837028","added_by":"auto","created_at":"2024-10-15 06:07:12","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":376399,"visible":true,"origin":"","legend":"\u003cp\u003eN\u003csub\u003e2\u003c/sub\u003e adsorption–desorption isotherms at 77 K of AC,\u003c/p\u003e\n\u003cp\u003eAC-Silica, AC-Lignin and AC-Silica-Lignin.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5034064/v1/270700968b2251495538499b.jpeg"},{"id":66640892,"identity":"dea3a5da-ff0e-4b11-bc8a-1b4b1cadb790","added_by":"auto","created_at":"2024-10-15 06:07:15","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":422545,"visible":true,"origin":"","legend":"\u003cp\u003eTGA/TDA curves of AC, AC-Lignin, AC-Silica and AC-Silica –Lignin.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5034064/v1/43aa7d40d10b61ee417d7129.jpeg"},{"id":69185348,"identity":"99eb00d2-265e-4244-9e78-25ec32c76dec","added_by":"auto","created_at":"2024-11-17 15:23:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1300016,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5034064/v1/9098fcef-2047-4e32-b7d0-f263a7437e49.pdf"}],"financialInterests":"","formattedTitle":"Carbon materials based on lignin and their environmentally friendly applications","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eCellulose and hemicellulose, lignin is a highly abundant biopolymer. As a major component of lignocellulosic materials, lignin accounts for a significant proportion of biomass including wood and agricultural residues. It has great potential for utilization as a green raw material or as an additive in various industrial applications, it can be used as an adhesive or tanning agent and it is used for paper industry (Tong H et al .2019). According to literature, much of the lignin produced by the paper industry is consumed as a fuel and the annual production of industrial lignin in the world is more than 70\u0026nbsp;million tons (De Wild P.J et al.2012, Suhas, P.J.M et al.2007).\u003c/p\u003e \u003cp\u003eOther applications such as production of activated carbons (ACs) and carbon fibers from lignin have also gained much interest in the last few years. Lignin has been proven to be a good source for producing activated carbons using chemical activation methods. In addition to that, lignin has been used as a precursor or feedstock for the preparation of high-performance electrochemical energy materials and components such as electrodes, electrolyte additives, membrane separators, and binders.\u003c/p\u003e \u003cp\u003eTherefore, using waste biomass to produce activated carbons for water treatment is a potential method for comprehensive utilization of biomass waste. Olive stone is a waste, which is largely produced in the Mediterranean countries as Tunisia, where there are more than 60\u0026nbsp;million olive trees (Hannachi H et al.2007). Tunisia is the world\u0026rsquo;s second largest olive oil producer and during olive oil production process approximately 35\u0026ndash;40 kg of olive pomace is released per 100 kg of olive, it represents roughly 10% by weight of olive \u003cb\u003e(\u003c/b\u003eSellami F et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The use of this solid waste as a precursor for the preparation of activated carbon produces not only a high-quality adsorbent with low inorganic content for the purification of contaminated environments, but also contributes to minimizing the environmental impact of solid wastes.\u003c/p\u003e \u003cp\u003eRecently, the modification of carbonaceous materials seems particularly promising for improving the absorbents affinity. The literature review shows that the modifications of AC surface improve the properties by different treatment applications such as carbon dioxide adsorption (Shafeeyan MS et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2010\u003c/span\u003e, Chiang Y-C et al.2017), removal of siloxanes from landfill gas \u003cb\u003e(\u003c/b\u003eGong H et al. 2007\u003cb\u003e)\u003c/b\u003e, removal of contaminants from aqueous solutions (Yin C.Y et al.2007, Suhas et al.2016\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eIn addition, the porous structure of activated carbon depends on the pore size: meso- and macropores allow the diffusion of charged species whereas micropores favor the accumulation of charged species so carbon materials prepared from olive stone can be used as electrodes \u003cb\u003e(\u003c/b\u003eJaouadi M. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eThe main objective of this work was to develop a new method for olive waste and lignin management by preparing activated carbon which modified by coating silica and lignin. But to our knowledge, studies focusing on preparing and modification of activated carbon by lignin are few. The prepared composites could use as an adsorbent, fuel or for energy storage (used as an electrode). The thermal behavior, the structure, the porosity, and the general composition were studied using TGA-DTA, FTIR spectroscopy, adsorption-desorption of N\u003csub\u003e2\u003c/sub\u003e at 77K, Boehm titration and the measure of pH\u003csub\u003ePZC\u003c/sub\u003e.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Synthesis of activated carbon and activated carbon coated by silica\u003c/h2\u003e \u003cp\u003eIn our previous work, an activated carbon was prepared from olive stones and modified by silica \u003cb\u003e(\u003c/b\u003eJaouadi, M., 2021\u003cb\u003e)\u003c/b\u003e. The carbon materials are referred in the text as \u0026ldquo;AC\u0026rsquo;\u0026rsquo; and \u0026ldquo;AC-Silica\u0026rdquo;.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e2.2 Modification the prepared carbon materials by lignin\u003c/h3\u003e\n\u003cp\u003e1 g of industrial lignin (Supplied by a nursery in Soliman-Tunisia, 33% of humic acid and 67% fulvic acid) was added to 1 g of AC and/ or AC-Silica, the mixture was stirred at 60\u0026deg;C during 12h. The composite AC-lignin was washed using distilled water.\u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Physico-chemical characterizations\u003c/h2\u003e \u003cp\u003eThe pH\u003csub\u003ePZC\u003c/sub\u003e values were determined by a mass titration method proposed by M.V Lopez and al. \u003cb\u003e(\u003c/b\u003eLopez-Ramon, M.V et al. 1999). Various amounts of carbon materials were put in 10mL of 0.1mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e NaCl solutions (prepared with boiled water). The bottles were sealed and shaken in a thermostat shaker overnight, the equilibrium pH values of the mixtures were measured, and the limiting pH was taken as the pH\u003csub\u003ePZC\u003c/sub\u003e. The functional (acidic) groups present on the surface were quantified by Boehm\u003cb\u003e\u0026lsquo;s\u003c/b\u003e titration \u003cb\u003e(\u003c/b\u003eStrelko V et al.2002\u003cb\u003e).\u003c/b\u003e Experimentally, 0.1 g of carbon materials powder was mixed with 20 mL of 0.02 mol.L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e aqueous solutions composed by either NaOH, Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e or NaHCO\u003csub\u003e3\u003c/sub\u003e reactants. The mixtures were stirred for 48 h at a constant speed of 150 rpm at room temperature. Then, the suspensions were filtered through 0.45 \u0026micro;m membrane filters (Millipore 405314). To determine the contents of oxygenated groups, back-titrations of the filtrate (10 mL) were performed with standardized HCl (0.02 mol. L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). The numbers of acidic sites were calculated by assuming that NaOH neutralizes the carboxyl, phenolic and lactonic groups, while Na\u003csub\u003e2\u003c/sub\u003eCO\u003csub\u003e3\u003c/sub\u003e neutralizes the carboxyl and lactonic groups, and NaHCO\u003csub\u003e3\u003c/sub\u003e neutralizes the carboxyl groups only. The characterization of prepared AC and AC-Si powders by Fourier transforms infrared (FT-IR) spectroscopy were performed using a Spectrum 100 FTIR spectrometer (PerkinElmer- France). The transmission spectra were recorded using KBr pellets. All spectra were obtained in the 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm \u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range at a resolution of 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The thermal analyses (TGA-DTA) of carboneous materials were carried out with a SETARAM apparatus. Experiments were performed under an argon gas at a heating rate of 5\u0026deg;C min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the temperature range of 25-1100\u0026deg;C by using 17.5 mg of each sample. The specific surface areas and pore size distributions were obtained from the adsorption/desorption isotherms of N\u003csub\u003e2\u003c/sub\u003e at 77 K using an automatic sorptometer (ASAP 2020, Micromeritics, USA). Prior to each measurement, the sample was degassed during 48h at 250\u0026deg;C for AC and 100\u0026deg;C for AC-Si, AC-lignin and AC-Silica-lignin to avoid the decomposition of the surface groups. Then, specific surface areas of prepared powders were calculated from the Brunauer-Emmett-Teller (BET) equation.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Characterization of the carbon materials\u003c/h2\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1. Boehm titrations and pH\u003csub\u003ePZC\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eThe pH\u003csub\u003ePZC\u003c/sub\u003e value of AC (2.25) is in agreement with the one (i.e. 3.7) measured by Clark et al. (Clark, H.M. et al. 2012) for an activated carbon prepared by H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e activation of coffee residues at 350\u0026deg;C.\u003c/p\u003e \u003cp\u003eThe pH\u003csub\u003ePZC\u003c/sub\u003e of AC increased after silica coating (2.6). For such low values (pH\u003csub\u003ePZC\u003c/sub\u003e \u0026lt; 4.5, (Kosmulski M. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2002\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e, amphoteric silanol groups are deprotonated and the net surface charge is negative over a wide pH range. The low pH\u003csub\u003ePZC\u003c/sub\u003e values for all carbon materials are generally associated to the presence of acidic carboxylic functional groups.\u003c/p\u003e \u003cp\u003eThe pH\u003csub\u003ePZC\u003c/sub\u003e values were confirmed by the acidic character of activated carbons surface measured by Boehm titration\u0026lsquo;s method. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e indicates the amounts of carboxylic, phenolic, lactonic and acidic groups present on as-prepared carbonaceous surfaces. The AC-Silica and AC- Lignin-Silica surface present the highest amount of acidic groups. The increase in the content of oxygenated groups after the Si coating is mainly due to the formation of additional carboxylic groups.\u003c/p\u003e \u003cp\u003eAccording to Jaouadi et al. \u003cb\u003e(\u003c/b\u003eJaouadi, M et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) the increase of the content of oxygenated groups after the Si coating is mainly due to the formation of additional carboxylic groups that are beneficial for the hydrophilicity and wettability of carbonaceous surfaces, the AC-Silica and AC-lignin-Silica can be used as electrodes for electrochemical devices especially for supercapacitors.\u003c/p\u003e \u003cp\u003eAC has a small quantity of phenolic groups, which confirms that after preparation of activated carbon from olive wastes (olive stone) the phenolic groups were removed. The study of Monetta et al. \u003cb\u003e(\u003c/b\u003eMonetta P et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) confirmed that olive wastes when applied, as a soil amendment produce a high increase in polyphenol levels, so preparing an activated carbon from olive stones will remove phenolic compounds.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003epH\u003csub\u003ePZC\u003c/sub\u003e, total surface acid groups of the carbon materials (mmol/g : determined by Boehm titrations).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003epH\u003csub\u003ePZC\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCarboxylic\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePhenolic\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLactonic\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAcidic\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAC-Silica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAC-Lignin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAC-Lignin-Silica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2.63\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1.2. FTIR analyses\u003c/h2\u003e \u003cp\u003eFTIR spectra of AC, AC-Silica, AC-Lignin and AC-Lignin-Silica are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. For all the samples, the stretching vibrations of -OH groups (υ\u003csub\u003eOH\u003c/sub\u003e), observed around 3500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, are attributed to the adsorbed residual water on carbons and are related to the hydrogen bond formed by the association of O-H, and the peak at 3290 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e were verified to be the hydroxyl association belongs to carboxylic acid. For AC-Silica-Lignin and AC-Lignin the high intensity of this υ\u003csub\u003eOH\u003c/sub\u003e band could be related to the high amount of phenolic groups in this material. For both samples, the band at 1700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (υ\u003csub\u003eC=O\u003c/sub\u003e) is assigned to the C\u0026thinsp;=\u0026thinsp;O stretching vibrations of ketones, aldehydes, lactones or carboxyl groups \u003cb\u003e(\u003c/b\u003eStrelko V. 2002\u003cb\u003e)\u003c/b\u003e. The broad band at 1000\u0026ndash;1300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (maxima at 1190\u0026ndash;1200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) has been assigned to C-O stretching in acids, alcohols, phenols, ethers and/or esters groups \u003cb\u003e(\u003c/b\u003eJaouadi M et al.2021\u003cb\u003e)\u003c/b\u003e. This band is particularly more intense for AC-Si. The strong C-O-C stretching bands (υ\u003csub\u003eC\u0026minus;O\u0026minus;C\u003c/sub\u003e) were also observed from 1100 to 1200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for AC-Silica, indicating the presence of aromatic ether or ester bond. The presence of Si in AC-Si composites is confirmed by the weak band located at 955 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, ascribed to Si-O-H asymmetry stretching and bending vibration, and bands at 1090 and 650 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to Si-O-Si asymmetric and symmetric stretching, respectively \u003cb\u003e(\u003c/b\u003eJaouadi, M et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe peak at 1030 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e appeared in the AC-Silica-Lignin and AC-Lignin was ascribed to the C-OH and C\u0026ndash;O-C stretching of the side groups and glycosidic bonds, respectively \u003cb\u003e[18]\u003c/b\u003e. The intensity at 1461 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e in both carbon materials modified by lignin was attributed to the methoxy C\u0026ndash;H bending and C\u0026ndash;C stretching in the aromatic skeleton \u003cb\u003e(\u003c/b\u003e Shi Z et al.2019\u003cb\u003e)\u003c/b\u003e. It can be found that the characteristic peaks corresponding to lignin appeared in AC-Lignin and AC-Silica-Lignin, these phenomena confirmed the reaction between lignin and carbon materials.\u003c/p\u003e \u003cp\u003eLignin contains phenolic component and the presence of several functional groups (OH, COOH, and C\u0026thinsp;=\u0026thinsp;O), lignin has the potential to be valorized for bio-composites and antioxidant materials \u003cb\u003e(\u003c/b\u003eUmme M. A et al. 2021). These are useful in the agroindustry as additives, coating agents, adsorbents, plant growth stimulators for food production, packaging materials, and fertilizers \u003cb\u003e(\u003c/b\u003eMaurice N.C et al. 2020\u003cb\u003e).\u003c/b\u003e Therefore, carbon materials modified by lignin probably play the same role of lignin.\u003c/p\u003e \u003cp\u003eAnother side, oxygen-containing functional groups found in carbon material surfaces play a vital role in the adsorption. Notably, the peaks of the -OH, -COOH groups displayed the adsorption of heavy metal ions due to the possible formation of complexes with them \u003cb\u003e(\u003c/b\u003eZawadzki J.1989\u003cb\u003e).\u003c/b\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1.3. Porosity characterization\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the N\u003csub\u003e2\u003c/sub\u003e adsorption\u0026ndash;desorption isotherms (at 77 K) of AC, AC-Silica, AC-Lignin and AC-Silica-Lignin. The isotherms of AC, AC-Silica exhibit an IV\u0026ndash;type profile that reflects the existence of micro- and mesopores. The isotherms of AC-Lignin and AC-Silica-Lignin are type I and typical of mainly microporous activated carbons. In the AC-Lignin and AC-Silica-Lignin composites the volume has sharply decreased compared to AC and AC-Silica (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe BET specific surface area (Table\u0026nbsp;3) was decreased after lignin reaction with AC and AC-Silica (from 957.26 to 642.5 and from 902 to 375. 12 m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively) because the pores were either collapsed or blocked after strong reaction with lignin. The AC-Silica-Lignin composite showed a low specific surface, which indicated that free pores of activated carbon were occupied by silica upon modification and pores of AC-Silica, was also covered by lignin upon reaction. Probably the component of lignocellulosic precursors found in lignin primarily responsible for the microporosity of activated carbons \u003cb\u003e(\u003c/b\u003eSuhas, P.J.M et al. 2007\u003cb\u003e).\u003c/b\u003e\u003c/p\u003e \u003cp\u003eAccording to Wang et al. (Wang X et al.2018) lignin has been considered as the substrate of adsorbents because of its low price and easy modification, most importantly, its ability to accelerate the adsorption rate of heavy metal ions (Wang X at al.2021). The prepared activated carbon can be used as adsorbents or as electrodes for energy storage. The mesoporous structure is expected to improve the electrochemical performance by enhancing the ionic mobility, while micropores are more efficient for the charge accumulation. In the same way, the wettability of the electrode may be affected by the size of electrolyte ions in regards to the pore size of the surface \u003cb\u003e(\u003c/b\u003eChmiola J et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePorosity characteristics of AC, AC-Lignin, AC-Silica and AC-Silica-Lignin.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eSurface area S\u003csub\u003eBET\u003c/sub\u003e (m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePore volume V\u003csub\u003etot\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(cm\u0026sup3;.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMicropore\u003c/p\u003e \u003cp\u003earea\u003c/p\u003e \u003cp\u003e(m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMesopore area\u003c/p\u003e \u003cp\u003e(m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eExternal\u003c/p\u003e \u003cp\u003earea\u003c/p\u003e \u003cp\u003e(m\u003csup\u003e2\u003c/sup\u003e.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMicropore volume V\u003csub\u003em\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(cm\u0026sup3;.g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e957.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e601.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e355.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e355.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAC-lignin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e642.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e565.35\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e77.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e77.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAC-Silica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e902\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e550.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e351.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e351.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eAC-Silica-Lignin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e375.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e304.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e70.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e70.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAC-Silica, AC-Lignin and AC-Silica-Lignin.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.1.4 TGA-DTA analyses\u003c/h2\u003e \u003cp\u003eThe thermal stability of electrode materials is a significant parameter. Hence, TGA/TDA measurements were carried out for AC, AC-Silica, AC-Lignin and AC-Silica-Lignin powders as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The weight losses carbon materials are mainly embodied in the temperature range over 120\u0026deg;C and attributed to the decomposition of carbon frameworks \u003cb\u003e(\u003c/b\u003eZawadzki J. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1989\u003c/span\u003e\u003cb\u003e).\u003c/b\u003e The weight losses of AC, AC-Silica, AC-Lignin and AC-Silica-Lignin are established in three stages; when the temperature is below 150\u0026deg;C, the weight loss of \u003cb\u003e~\u003c/b\u003e\u0026thinsp;20% is caused by the desorption of water. From 150 to 500\u0026deg;C, the loss is about\u0026thinsp;\u003cb\u003e~\u003c/b\u003e\u0026thinsp;10% and results from the decomposition of oxygenated functional groups. From 500 to 1100\u0026deg;C, the weight loss is about 13, 20, 20 and 14% for AC, AC-Silica, AC-Lignin and AC-Silica-Lignin, respectively. This weight loss corresponds to the decomposition of the organic compounds. It is noticed that DTA curves of AC, AC-Silica samples present very similar decomposition profiles. The endothermic transition at 120\u0026deg;C, due to water vaporization, is followed by an exothermal transition at 450\u0026deg;C. For AC-Lignin and AC-Lignin-Silica, the exothermal transition at 450\u0026deg; was disappeared after reaction with lignin.\u003c/p\u003e \u003cp\u003eThe DTA curves of carbon materials modified by lignin (AC-Lignin and AC-Lignin-Silica) analyzed in this work, shows an endothermic peak between 400 and 1000\u0026deg;C, which may be assigned to decarboxylation reactions \u003cb\u003e(\u003c/b\u003eJaouadi M. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003cb\u003e).\u003c/b\u003e Lignin has special features such as thermal stability and can be used a compost.Industrial lignin is currently not fully utilized. A large amount of industrial lignin is discarded as waste or burned only as a low-value fuel.\u003c/p\u003e \u003cp\u003eIn short, the addition of lignin in AC and in AC-Silica enhanced the overall thermal stability of the adsorbents, and confirmed that lignin was successfully grafted onto the carbon materials (AC and AC-Silica). On the other hand, carbon materials modified by lignin can be consumed as a fuel. The main advantage of coating of lignin into carbon surfaces is to reduce the high ash fractions and to increase the energetic density. Hence, Tunisia and other emerging countries, lacking sources of classic fossil fuels can base energy policy on economic and sustainable alternatives like agropellets.\u003c/p\u003e \u003cp\u003eSeveral authors described the thermal degradation as a progressive decomposition of their cellulose, hemicelluloses and lignin \u003cb\u003e(\u003c/b\u003eOuatmane A et al.2000).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eOlive wastes and lignin were key compounds and have a great importance for the development of sustainable biomass valorization and they were successfully developed. FTIR results show the presence of some active functional groups, which play a vital role in the adsorption and confirm that modified carbon by lignin, can be used as plant growth stimulators and fertilizers. Boehm titration shows the increase of phenolic groups in carbon based lignin, which confirms that lignin has the potential to be valorized for bio-composites and antioxidant materials. The thermal analyses show the high stability after lignin coating so the carbon based on lignin can be used as a green biofuel. Carbon based on lignin can be used as electrodes for energy storage.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by research program of the Tunisian Ministry of Higher Education\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of interest/ Competing interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated and analyzed during the current study are included in this article\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor\u0026rsquo;s contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMouna Jaouadi:\u0026nbsp;\u003c/strong\u003eMaterial preparation, Materials characterization, original draft preparation, Reviewing and supervision.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChiang Y-C, Juang RS (2017) Surface modifications of carbonaceous materials for carbon dioxide adsorption: a review. 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Marcel Dekker, New York, 1989 pp 147\u0026ndash;3860\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Lignin, olive stone, activated carbon, valorization, adsorption","lastPublishedDoi":"10.21203/rs.3.rs-5034064/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5034064/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe green revolution concept has accelerated the pace of innovation to avoid the use of materials that can harm the environment. In this work, the valorization of lignin and olive wastes was studied. Olive stone used to prepare activated carbons which are modified by lignin. The carbons were characterized by TGA-DTA, FTIR spectroscopy, adsorption-desorption of N\u003csub\u003e2\u003c/sub\u003e at 77K, Boehm titration and the measure of pH\u003csub\u003ePZC\u003c/sub\u003e. FTIR results show the presence of some groups that confirm that carbons based lignin can be used as fertilizers. BET results show micro- mesoporous structure of carbons materials, they might be used as electrodes. Boehm titration shows the increase of phenolic groups in modified carbon, which confirms that lignin can be used as bio-composites. The thermal analyses show the high stability after lignin coating so the carbon based on lignin can be used as a green biofuel.\u003c/p\u003e","manuscriptTitle":"Carbon materials based on lignin and their environmentally friendly applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-15 06:03:26","doi":"10.21203/rs.3.rs-5034064/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d7388400-dc27-4c14-98f9-e0742049ff67","owner":[],"postedDate":"October 15th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-11-17T15:15:47+00:00","versionOfRecord":[],"versionCreatedAt":"2024-10-15 06:03:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5034064","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5034064","identity":"rs-5034064","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}