C@TiO2 core-shell adsorbents for efficient rhodamine B adsorption from aqueous solution

In the present work, C@TiO2 core-shell adsorbents were successfully prepared and the adsorption capacities for rhodamine B (RB) were investigated at different conditions. The adsorbents were prepared by first in-situ hydrolysis and deposition of TBOT on the surface of ZIF-8 nanoparticles to obtain ZIF-8@titania gel, and then carbonization.

Microporous and Mesoporous Materials 320 (2021) 111110 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: http://www.elsevier.com/locate/micromeso C@TiO2 core-shell adsorbents for efficient rhodamine B adsorption from aqueous solution Kang Li a, Liang Yu b, *, Juanjuan Cai a, Lixiong Zhang a, ** a b State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Tech University, Nanjing, 211816, China Chemical Technology, Luleå University of Technology, SE-971 87, Luleå, Sweden A R T I C L E I N F O A B S T R A C T Keywords: ZIF-8 Titania C@TiO2 adsorbents Rhodamine B Wastewater treatment In the present work, C@TiO2 core-shell adsorbents were successfully prepared and the adsorption capacities for rhodamine B (RB) were investigated at different conditions The adsorbents were prepared by first in-situ hy­ drolysis and deposition of TBOT on the surface of ZIF-8 nanoparticles to obtain ZIF-8@titania gel, and then carbonization XRD, SEM, TEM, and N2 adsorption-desorption techniques were employed to characterize the adsorbents The results showed that the adsorbents were comprised of TiO2 shell and carbon core Large surface area and hierarchical pores, which were different from ZIF-8 derived porous carbon, were generated due to the less contraction of carbon during carbonization when robust TiO2 shell covered on the surface The highest adsorption capacity for RB was 298 mg/g on C@TiO2 Apart from the hierarchical pores and large surface area, the low surface charge of C@TiO2 core-shell adsorbents was also observed, which also contributed to the high adsorption capacity for cationic dyes The reuse experiments showed that the adsorbents maintained the high adsorption capacity after cycles The high stability is crucial for practical application Introduction Adsorption, as an efficient process for wastewater treatment, has drawn much research attention Therefore, the development of high performance and cost-effective adsorbents for the removal of organic contaminants like dyes from textile dyeing effluents are of a great in­ terest [1–3] Porous carbons have been considered as efficient adsor­ bents for various adsorption applications due to the porous structure, high stability and environmentally friendly properties However, microporous biochar [4] and activated carbon [5] displayed low adsorption capacities of 86 and 55 mg/g, respectively, for RB The low adsorption capacity resulted from the small pore size Higher adsorption capacities of 284 and 423 mg/g were observed for brilliant yellow and RB on mesoporous carbons due to the larger pore size and pore volume [6] Graphene-like porous carbon with even higher surface area (1710 m2/g) and pore volume (0.83 cm3/g) showed excellent adsorption ca­ pacity of 418 mg/g for methyl orange [7] However, for many carbon materials, the preparation procedures were complicated and the im­ provements of pore systems and surface chemistry are needed from higher adsorption performance Many methods have been developed to prepare carbons with unique structures [8] and surface chemistry for higher adsorption capacity [9] Carbon composites combined the advantage of at least two materials, which could display significantly higher adsorption capacity than the single component materials For instance, porous carbon nanosheets (PCNSs) comprised of two different carbons sources were prepared by carbonizing of waste plastics covered organically-modified montmoril­ lonite The surface area (2315 m2/g) and pore volume (3.3 cm3/g) of the carbon materials were large, and the surface zeta potential was low Therefore, the adsorption capacity for methylene blue was unprece­ dentedly high about 769 mg/g [10] For RB adsorption, an adsorption capacity of 625 mg/g on montmorillonite/graphene oxide nano­ composites was observed, which was higher than that of montmoril­ lonite and graphene oxide [11] The synergistic effect of the components in the nanocomposites contributed to the high adsorption capacity [11] In addition, composites could generate hierarchically structured porous materials, which can improve the mass transfer efficiently Our group also developed several composites that showed high performance for gas upgrading and wastewater treatment For example, NaX/NaA core-shell microspheres showed a higher adsorption * Corresponding author ** Corresponding author E-mail addresses: liang.yu@ltu.se, yuliangchem@yahoo.com (L Yu), lixiongzhang@yahoo.com (L Zhang) https://doi.org/10.1016/j.micromeso.2021.111110 Received 15 February 2021; Received in revised form 20 March 2021; Accepted 13 April 2021 Available online 16 April 2021 1387-1811/© 2021 The Authors Published by Elsevier Inc This is an (http://creativecommons.org/licenses/by-nc-nd/4.0/) open access article under the CC BY-NC-ND license K Li et al Microporous and Mesoporous Materials 320 (2021) 111110 Experimental 2.1 Synthesis of ZIF-8 nanoparticles The detailed procedures for the preparation of ZIF-8 have been described in literature [18] Briefly, dissolved 2.3 g Zn(NO3)2•6H2O and 32 g 2-methylimidazole in 16 and 112 g water, respectively Afterward, the 2-methylimidazole aqueous solution was added into the Zn (NO3)2•6H2O aqueous solution quickly under vigorous stirring condi­ tions The centrifuge was used to recover the product after stirring for h and then freezing dry 2.2 Preparation of TiO2 coated carbon nanoparticles The obtained ZIF-8 (0.1g) was dispersed in 40 ml ethanol and added 0.062 g tetrabutyl orthotitanate (TBOT) under stirring condition The mass ratio of ZIF-8 and TBOT was 1:0.62 After stirring for h, 70 ml water was added into the solution using a syringe pump The flowrate was ml/min Then, the mixture was stirred for 12 h at room temper­ ature The obtained product was recovered by centrifuge The sample was denoted as ZIF-8@titania gel-1 Meanwhile, ZIF-8@titania gel-2 and ZIF-8@titania gel-3 were also prepared using the mass ratio of ZIF-8 and TBOT of 1:1.25 and 1:2.50, respectively ZIF-8@titania gel-1, ZIF-8@titania gel-2, and ZIF-8@titania gel-3 were carbonized under nitrogen atmosphere to obtain C@TiO2-1, C@TiO2-2, and C@TiO2-3, respectively The carbonization temperature was 700 ◦ C and the time was h ZIF-8@titania gel-2 sample was also carbonized at 850 and 1000 ◦ C to investigate the effect of carbonization temperature, the obtained products were denoted as C@TiO2-850 and C@TiO2-1000, respectively Fig Observed XRD patterns of as-synthesized titania gel, ZIF-8@titania gel2, and ZIF-8 Blue bars represent the reference XRD pattern of ZIF-8 (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) selectivity for CO2/N2 compared to NaX microspheres [12] Hollow zeolite NaA/chitosan composite microspheres prepared in a simple microchannel device showed an adsorption capacity of 16 mg/g for Cu2+ from water at the studied conditions [13] Carbon/cobalt com­ posites were simply prepared by carbonization the mixtures of phenolic resin and ZIF-67 The composites displayed high adsorption capacity of 2778 mg/g for tannic acid In contrast, the adsorption capacity was 205 and 1375 mg/g on phenolic resin and ZIF-67 derived carbons, respec­ tively [14] Core-shell composites prepared by coating one component on the surface of the other can exhibit different properties for different applications due to the change of the surface chemistry [15] Recently, we reported a C@silica core-shell adsorbent for the adsorption of cip­ rofloxacin [16] ZIF-8 was used as the carbon source Moreover, ZIF-8 is a microporous metal-organic framework material composing of Zn cat­ ions coordinated to 2-methyimodazole linkers The observed adsorption capacity was1575 mg/g at the optimum adsorption conditions Besides, the results also showed that the charge on the core-shell nanoparticles was more negatively due to the effect of silica shell, thereby improving the adsorption capacity Very recently, we also reported a porous C@C composite adsorbent for the adsorption of dye contaminants from water The adsorbents were prepared from the carbonization of resorci­ nol–formaldehyde (RF) resins@ZIF-8 composites [17] The surface area of the C@C composite adsorbent was much higher than the single components derived carbons Meanwhile, the pore size of the C@C composite adsorbent was slightly larger Therefore, the adsorption ca­ pacities of the composite adsorbents for methylene blue and RB was as high as 681 and 462 mg/g, respectively Interestingly, the results also showed a lower surface charge on composite, which also enhanced the adsorption All the developed composites displayed high stability and could be recycled easily, meanwhile, maintained high adsorption ca­ pacity In addition, the results also indicated that surface modification is an efficient method for the preparation of high performance adsorbents In the present work, we prepared C@TiO2 core-shell adsorbents by carbonizing ZIF-8@titania gel core-shell composites The titania gel coated on the surface ZIF-8 particles by hydrolysing and depositing TBOT To optimize the preparation conditions, different ratios of TBOT to ZIF-8 and carbonization temperatures were investigated The effect of TiO2 shell on the pores and surface chemistry of ZIF-8 derived porous carbon were explored The obtained composites were used for RB adsorption and the adsorption conditions were optimized Meanwhile, the adsorption mechanism was discussed 2.3 Adsorption experiments All adsorption experiments were carried out at 30 ◦ C and the tem­ perature of the solution was controlled by an oil bath C@TiO2 nano­ particles (2.5 mg) were added in 50 ml RB aqueous solutions with the concentration of 40 mg/l for adsorption Sodium hydroxide (0.1 M) or hydrogen chloride (0.1 M) aqueous solution was used to adjust the pH The adsorption loading at different adsorption times was determined by analysis of ml solution taken from the bulk solution Prior to analysis, the collected solutions were filtered using 10 μm filter and diluted 10 times RB aqueous solutions with the concentration from 20 to 100 mg/l were used to determine the adsorption isotherms A MAPADA UV-1800 PC spectrophotometer was employed for the determination of RB con­ centration at a wavelength of 544 nm The adsorption loading q for RB was defined as: q= V (C0 − Ct ) m Where V (ml) is RB aqueous solution volume, m (mg) is the mass of C@TiO2 used for adsorption, C0 (mg/l) and Ct (mg/l) are the concen­ tration of RB before and after adsorption 2.4 Materials characterizations Bruker D8 Advance powder X-ray diffractometer (Cu target) was used to record XRD patterns with the tube voltage and current of 40 kV and 40 mA, respectively SEM images was recorded using a field emis­ sion scanning electron microscope (Hitachi− S4800) JEOL JEM-2100 transmission electron microscope was employed to recorded TEM im­ ages BELSORP II instrument was used to measure the N2 adsorptiondesorption isotherms at 77 K The samples were treated at 150 ◦ C for h under vacuum before the measurement The BET method was used to calculate the surface area and the total pore volume was estimated at p/ p0 of 0.99 K Li et al Microporous and Mesoporous Materials 320 (2021) 111110 Fig Morphology of titania gel (a), ZIF-8 (b), and ZIF-8@titania gel-2 (c) observed by SEM Fig XRD patterns (a) and SEM images of ZIF-8@titania gel-1 (b) and ZIF-8@titania gel-3 (c) Results and discussion ethoxy group (CH3CH2O–) that presented on the surface of the hydro­ lysed titania gel and affected the phase change of the gel during drying [20] SEM images of titania gel, ZIF-8, and ZIF-8@titania gel-2 are given in Fig The SEM image of titania gel shows a structure of agglomerate particles and uneven size The size of the crystals has not changed obviously indicated that a thin titania gel layer covered on ZIF-8 crys­ tals Therefore, the morphology of ZIF-8 crystals was preserved in ZIF8@titania gel-2 To identify the particle sizes of the obtained samples, 100 particles from each SEM image were measured, and the average particle sizes of 78 ± 17 and 106 ± 20 nm were obtained for ZIF-8 3.1 ZIF-8@titania gels particles As shown in Fig 1, the crystalline structures of the prepared titania gel, ZIF-8, ZIF-8@titania gel-2 were characterized by XRD The XRD pattern indicates a high quality ZIF-8 that is confirmed by the simulated XRD pattern of ZIF-8 as indicated by blue bars [19] No impurity peak was detected Due to the effect of amorphous titania gel, the peaks in­ tensity of the ZIF-8 became weaker after coating with titania gel Moreover, the amorphous structure of titania gel resulted from the K Li et al Microporous and Mesoporous Materials 320 (2021) 111110 Fig XRD (a), SEM image of TiO2 (b), C (ZIF-8) (c) and C@TiO2-2 (d) as well as TEM image of C@TiO2-2 (e) Fig SEM images of C@TiO2-850 (a) and C@TiO2-1000 (b) crystals and ZIF-8@titania gel-2, respectively Therefore, the thickness of titania gel layer was about 14 nm More details about the structure of the ZIF-8@titania gel-2 will be discussed below ZIF-8@titania gel-1 and ZIF-8@titania gel-3 particles prepared from different mass ratios of ZIF-8 and TBOT were characterized by XRD and SEM The results are given in Fig The peaks intensity was weaker with the increase of TBOT due to the thicker titania gel shell on ZIF-8 crystals, meanwhile, the particles became more agglomerated The average particle size was about 82 ± 18 nm for ZIF-8@titania gel-1 and 120 ± 21 nm for ZIF-8@titania gel-3, the corresponding titania gel shell thickness was about and 21 nm, respectively 3.2 C@TiO2 particles The XRD patterns of C@TiO2-2, ZIF-8 derived porous carbon and pure TiO2 that were carbonized at 700 ◦ C under N2 atmosphere are shown in Fig 4a XRD pattern of the pure TiO2 shows a mixture of anatase and rutile phases This is different from that of the C@TiO2-2, which solely showed a rutile structure It is important to note that ZIF-8 derived porous carbon was an amorphous structure as indicated by XRD pattern Therefore, the differences of phases of TiO2 between pure TiO2 and C@TiO2-2 resulted from the effect of carbon on the phase trans­ formation of TiO2 at high temperature It has been reported that the K Li et al Microporous and Mesoporous Materials 320 (2021) 111110 Fig N2 adsorption-desorption isotherms of samples prepared at different conditions strong reducing agent, carbon could enhance the formation of oxygen vacancies in an inert atmosphere thereby promoting the reconstructive process [22] This could explain that almost only rutile was observed in the C@TiO2-2 composite The morphologies of titania gel and ZIF-8@titania gel-2 were pre­ served after high temperature treatment (see Figs and 4) For titania gel, carbonization could be considered as a deep drying process [23] Therefore, the morphology could probably be similar, i.e irregular shape, but smaller size Due to the stable structure of TiO2, the TiO2 shell could maintain the morphology of ZIF-8@titania gel-2 Therefore, the morphology of C@TiO2-2 was similar to ZIF-8@titania gel-2 after high temperature treatment Furthermore, TEM image in Fig 4e clearly shows a core-shell structure of C@TiO2-2 A rational hypothesis is that the core-shell structure comprised of a TiO2 shell with carbon core and the robust TiO2 shell maintained the morphology of ZIF-8@titania gel-2 Table Summary of the textural properties of materials prepared at different conditions Samples Surface area (m2/g) Total pore volume (cm3/g) Average pore size (nm) TiO2 C (ZIF-8) C@TiO2-1 C@TiO2-2 C@TiO2-3 C@TiO21000 21 496 371 264 113 516 0.1 0.6 1.2 0.8 0.5 1.0 n/a 3.9 12.4 11.7 16.0 7.4 Fig Effect of contact time on the adsorption capacity of ZIF-8 derived porous carbon, TiO2, C@TiO2-1, C@TiO2-2 and C@TiO2-3 for RB transformation from anatase to rutile is a reconstructive process In this process, the chemical bonds will be broken and reformed at high tem­ peratures (>600 ◦ C) [21] Apart from temperature, the particle size, atmosphere, and dopant will also affect the phase transformation As a Fig Adsorption capacity of C@TiO2 prepared at different carbonization temperatures for RB The precursor of C@TiO2 was ZIF-8@titania gel-2 Fig Adsorption of C@TiO2-2 for RB at different pH (a) and the zeta potential of ZIF-8 derived porous carbon and C@TiO2-2 as a function of pH (b) K Li et al Microporous and Mesoporous Materials 320 (2021) 111110 Fig 10 Langmuir (a) and Freundlich (b) linear fitting of adsorption data However, a different structure was observed for C@TiO2-1000, which could be ascribed to the zinc component in the ZIF-8@titania gel The zinc could be evaporated at carbonization temperature due to the low boiling point [24] Therefore, C@TiO2-1000 with a more porous struc­ ture was observed Fig shows N2 adsorption-desorption isotherms of C@TiO2-1, C@TiO2-2, C@TiO2-3, and C@TiO2-1000 as well as TiO2 and ZIF-8 derived porous carbon TiO2 showed the lowest adsorption for N2 due to the low surface area [25] The steep and high uptake at low relative pressure range (close to zero) indicated that ZIF-8 derived porous carbon has abundant micropores that was similar with that of activated carbons No hysteresis loop was observed for isotherms of ZIF-8 derived porous carbon that indicates a monomodal pore system Type IV adsorption isotherms were obtained for all core-shell composite adsorbents The adsorption isotherms of C@TiO2 showed high nitrogen adsorption ca­ pacity at low pressure range and large hysteresis loop that indicated the materials have abundant micropores and mesopores Meanwhile, the adsorption isotherms of the composites at p/p0 around one increased sharply, which resulted from the macropores Therefore, the results indicated that the synthesized core-shell composites were hierarchically porous materials The surface area of C (ZIF-8) was 496 m2/g (see Table 1), and it decreased when the TiO2 content increased at the carbonization tem­ perature of 700 ◦ C However, the surface area was significantly high for sample carbonized at 1000 ◦ C due to pores generated during evapora­ tion of zinc at high temperature (also see SEM image in Fig 5b) In addition, the total pore volumes and average pore sizes of core-shell adsorbents were much higher than that of C (ZIF-8) due to the support of TiO2 shell (see SEM images in Fig 4), i.e the robust TiO2 shell moderated the contraction of ZIF-8 derived porous carbon and preserved the pores at high temperature that could benefit the accommodation of large organic dyes molecules Therefore, improved the adsorption Table Different adsorbents for the adsorption of RB from aqueous solution Adsorbents pH Temperature (◦ C) Maximum adsorption capacity (mg/g) References Sago waste carbon Gg-cl-P (AA-co-AAm)/ Fe3O4 nanocomposite kaolinite Bagasse pith derived activated carbon Sodium montmorillonite Natural zeolite Humic acid (HA) modifying Fe3O4 nanoparticles Organo-vermiculites Treated rice husk-based activated carbon solid hazardous waste scrap tires derived activated carbon ZIF-8 derived porous carbon C@TiO2 core-shell adsorbents 30 25 16 529 [28] [29] 30 20 46 264 [30] [31] 30 38 [32] 50 70 38 162 [33] [34] 25 20 529 234 [35] [36] 25 307 [37] 30 66 This work 30 298 This work Moreover, the size of C@TiO2-2 was about 92 ± 22 nm and the shell thickness was about 12 nm The size was slightly smaller than that of ZIF-8@titania gel-2 due to the contraction during carbonization Without the support of TiO2 shell, many particles with collapsed struc­ ture were observed in ZIF-8 derived porous carbon (see Fig 4c) compared to the original ZIF-8 particles (see Fig 2b) The results also indicated a high stability of C@TiO2-2 SEM images of C@TiO2-850 and C@TiO2-1000 are shown in Fig C@TiO2-850 shows similar morphology to C@TiO2-2 (see Fig 4d) Fig 11 Reuse of C@TiO2-1000 for RB adsorption and the morphology of C@TiO2-1000 after times recycling K Li et al Microporous and Mesoporous Materials 320 (2021) 111110 3.3 Adsorption of RB The table shows that our core-shell adsorbents displayed decent adsorption capacity compared to the reported results in the literature \After adsorption experiment, the C@TiO2-1000 adsorbent was recovered using centrifuge and regenerated by ultrasonic in methanol for 30 Fig 11a shows that the observed maximum adsorption loading were 269, 278, 257, 262, 258 mg/g, respectively, for consecutive cycles The morphology of the adsorbent was preserved after times reuse that indicated a high stability, see Fig 11b This is important for the real application of the adsorbent As shown in Fig 7, the maximum loading of RB on the adsorbents C (ZIF-8 derived), TiO2, C@TiO2-1, C@TiO2-2, C@TiO2-3 were 66, 43, 125, 140 and 105 mg/g, respectively C@TiO2 showed significantly higher adsorption capacity for RB The adsorption capacities are higher than that of TiO2 and ZIF-8 derived porous carbon One of the most important factors for the high adsorption is the larger pore size of the C@TiO2 composites as shown in Table In addition, the effect of TiO2 on the surface chemistry of carbon could affect the adsorption To optimize the adsorption capacity, adsorption at different condi­ tions, e.g pH, temperatures, concentrations of RB were investigated C@TiO2-2 was used as the adsorbent Fig 8a shows that the adsorption capacity was affected by pH significantly The adsorption loading was only 29 mg/g at pH of and the loading increased when the pH increased from to The maximum adsorption loading of 161 mg/g was observed at pH of 7, and the adsorption loading decreased to 120 mg/g when the pH further increased to The change of the adsorption loading with pH was ascribed to the different zeta potential of the adsorbent at different pHs Fig 8b shows that the lower zeta potential of C@TiO2 composite was observed at higher pH The minimum zeta po­ tential was − 43 mV at pH that would maximize the high adsorption for cationic RB In addition, zeta potential of the C@TiO2 was lower than ZIF-8 derived porous carbon due to the presence of TiO2 [26] The zeta potential of TiO2 decreased dramatically with the increase in the pH has been reported and a negative charge was obtained when pH higher than [26] Besides, in the pH range of 1–9, the lowest zeta potential of ZIF-8 derived porous carbon was observed at a pH of about [27], which is similar to the results observed in the present work Therefore, apart from the effect of robust TiO2 shell on the pores of ZIF-8 derived porous carbon as discussed above, the ZIF-8 derived porous carbon in combi­ nation with TiO2 could generate an adsorbent with lower zeta potential Therefore, C@TiO2 core-shell adsorbents showed higher adsorption performance for cationic dye RB Our previous work [17] showed that the carbonization temperature could affect the adsorption capacity of the carbon-based adsorbent The effect was also investigated in the present work Fig shows the results when ZIF-8@titania gel-2 was used as the precursor The maximum adsorption loading was higher for adsorbent prepared at higher carbonization temperature The adsorption loading was as high as 269 mg/g for C@TiO2 prepared at 1000 ◦ C (C@TiO2-1000) that was twofold of the adsorption loading of C@TiO2 prepared at 700 ◦ C As shown in Table 1, C@TiO2 core-shell adsorbent displayed higher surface area and pore volume when the carbonization temperature was higher This could explain the high adsorption capacity of C@TiO2-1000 To explore the adsorption process, the type of adsorption of RB on C@TiO2 composites was estimated using Langmuir and Freundlich models The details of these models can be found in the supporting in­ formation C@TiO2-1000 was used as an example due to the highest adsorption loading as shown above RB aqueous with different con­ centrations was used for the adsorption experiments The adsorption results can be found in Fig S2a The equilibrium adsorption capacity, i e the maximum adsorption loading was higher when the RB concen­ tration was higher For instance, the observed maximum adsorption loading was 258 mg/g for a 20 mg/l RB concentration, and it increased to 298 mg/g when the RB concentration increased to 100 mg/g Fig 10 shows the Langmuir and Freundlich linear fitting results The adsorption isotherm is shown in Fig S2b Table S1 summarizes the fitting constants The results in Fig 10 clearly show that the adsorption isotherms could be described by Langmuir isotherm model The estimated maximum adsorption loading was 322 mg/g that was slightly higher than the experimental results of 298 mg/g The modelling results indi­ cated that the adsorption should be homogeneous monolayer adsorp­ tion This resulted from the electrostatic interaction between cationic RB molecules and negatively charged surface of adsorbents Table sum­ marizes the typical adsorption capacities of different adsorbents for RB Conclusions C@TiO2 core-shell adsorbents have been successfully prepared by carbonizing ZIF-8@titania gels The adsorbents displayed a hierar­ chically porous structure The observed RB adsorption capacity of the core-shell adsorbents was much higher than that of C (ZIF-8) and TiO2 The robust TiO2 shell moderated the contraction of ZIF-8 derived carbon and preserved the pores during carbonization Carbonization tempera­ ture and pH of RB aqueous solution are crucial for the adsorption per­ formance The surface areas and total pore volumes of the prepared core-shell adsorbents were higher at higher carbonization tempera­ ture, which increased the adsorption capacity The adsorbents showed the maximum adsorption loading for RB at pH due the lowest zeta potential A monolayer adsorption state was confirmed by the Langmuir model Due to the robust TiO2 shell, the composite adsorbents showed high stability that makes the materials promising for practical application CRediT authorship contribution statement Kang Li: Investigation, Formal analysis, Writing – original draft Liang Yu: Conceptualization, Formal analysis, Validation, Visualiza­ tion, Writing – original draft, Writing – review & editing, Resources Juanjuan Cai: Investigation, Formal analysis Lixiong Zhang: Conceptualization, Supervision, Writing – review & editing, Funding acquisition Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Acknowledgements The Priority Academic Program Development of Jiangsu Higher Education Institutions is acknowledged for financially supporting this work Appendix A Supplementary data Supplementary data to this article can be found online at https://doi org/10.1016/j.micromeso.2021.111110 References [1] S.C Smith, D.F Rodrigues, Carbon 91 (2015) 122–143, https://doi.org/10.1016/j carbon.2015.04.043 [2] S De Gisi, G Lofrano, M Grassi, M 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reconstructive process In this process, the chemical bonds will be broken and reformed at... generate an adsorbent with lower zeta potential Therefore, C@TiO2 core-shell adsorbents showed higher adsorption performance for cationic dye RB Our previous work [17] showed that the carbonization