Lanthanum (La)-based nanoparticles (NPs) are promising candidates for phosphate removal owing to their inherently high affinity towards phosphate. However, significant challenges remain to be addressed before their practical deployment, especially the problems associated with their aggregation.
Carbohydrate Polymers 298 (2022) 120135 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Porous fibrous bacterial cellulose/La(OH)3 membrane for superior phosphate removal from water Liping Tan a, b, 1, Weihua Zhang a, 1, Xiaoguang Zhu a, Yue Ru a, Wenbo Yi a, Bo Pang c, *, Tongjun Liu a, * a Shandong Provincial Key Laboratory of Microbial Engineering, Department of Bioengineering, Qilu University of Technology, Shandong Academy of Sciences, Jinan 250353, China Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, College of Light Industry and Food Engineering, Guangxi University, Nanning 530004, China c Department of Materials and Environmental Chemistry, Stockholm University, Stockholm 10691, Sweden b A R T I C L E I N F O A B S T R A C T Keywords: Adsorption Bacterial cellulose Lanthanum hydroxide nanoparticles Phosphate removal Lanthanum (La)-based nanoparticles (NPs) are promising candidates for phosphate removal owing to their inherently high affinity towards phosphate However, significant challenges remain to be addressed before their practical deployment, especially the problems associated with their aggregation Herein, we fabricated a highefficient sorbent for phosphate removal through in-situ synthesizing La(OH)3 NPs on a natural support, bacte rial cellulose (BC), which is pre-modified with polyethyleneimine The resultant La(OH)3 NPs-immobilized BC with different La contents (BPLa-X) exhibited a highly fibrous porous structure, in which BPLa-3 was selected for further phosphate adsorption studies BPLa-3 demonstrated a high adsorption capacity of 125.5 mg P g− 1, and high adsorption selectivity due to the large surface area and abundant exposed active adsorption sites for phosphate Additionally, BPLa-3 also displayed high reusability and still possessed high adsorption capacity after four consecutive cycles of adsorption-desorption Therefore, the present adsorbent is believed to be a promising candidate for practical phosphate removal Introduction Phosphorus (P) being a structural and functional component of nucleic acids, phosphor-proteins and enzymes is an essential element of various living organisms (Adam, Peplinski, Michaelis, Kley, & Simon, 2009; Correll, 1998; Paytan & McLaughlin, 2007) However, excessive amounts of such a crucial element in water bodies can cause serious environmental problems, for example, eutrophication and major eco nomic losses (Conley et al., 2009; Li, Chen, Zhao, & Zhang, 2015) Removing and recovering P from water/wastewater has been recog nized as one of the most promising approaches to addressing these challenges To date, various approaches including chemical precipita tion (Gaterell, Gay, Wilson, Gochin, & Lester, 2000), biological treat ment (Lv, Yuan, Chen, Liu, & Luo, 2014), adsorption (Chen et al., 2018), and/or combinations of these technologies have been developed for P removal and recovery in the field of agricultural, industrial or domestic wastewater treatment (Chen et al., 2018; Mino, Van Loosdrecht, & ˘uz, Gürses, & Canpolat, 2003; Qu et al., 2022) Bio Heijnen, 1998; Og logical treatment generally exhibits high efficiency with reduced chemical costs but is highly sensitive to pollution loading variations and influent flow (Oehmen et al., 2007; Yeoman, Stephenson, Lester, & Perry, 1988) Although chemical precipitation has been recognized as an effective and low-cost method, secondary pollution may occur due to excessive amounts of waste disposals and undesired chemicals gener ated during such processes (Chen et al., 2018) Compared with these methods, adsorption approaches relying on the utilization of functional materials with high affinity for P are preferred owing to various merits such as high efficiency, low cost, and high practicability (Zhang et al., 2022) Lanthanum, an abundant rare-earth element considered to be envi ronmentally friendly, has inherently high affinity for phosphate and can form complexes with phosphate of low concentrations (Yang et al., 2011; Yang et al., 2012) Note: P exists in nature dominantly in the form of phosphate, which is also the only form of P that can be directly * Corresponding authors E-mail addresses: bo.pang@mmk.su.se (B Pang), liutongjun@outlook.com (T Liu) Equally contributed first-authors https://doi.org/10.1016/j.carbpol.2022.120135 Received 10 July 2022; Received in revised form 13 September 2022; Accepted 18 September 2022 Available online 21 September 2022 0144-8617/© 2022 The Authors Published by Elsevier Ltd This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/) L Tan et al Carbohydrate Polymers 298 (2022) 120135 assimilated by algae, microorganisms and many other planktons Until now, various types of lanthanum-containing materials, especially lanthanum-based micro/nanoparticles such as La(OH)3 and La2O3 have been developed for removing and recovering phosphate (Razanajatovo et al., 2021; Zhi et al., 2020) However, similar to many other kinds of micro/nanoparticles, La-based micro/nanoparticles (La-M/NPs) also tend to form aggregates due to their high surface energy, which will inhibit the efficient utilization of the inner regions of the resulting ag gregates (Cumbal & SenGupta, 2005; Tesh & Scott, 2014; Zhang, Xu, et al., 2022) In addition, these La-based particles are not easy to be recycled from the water environment after use Loading La-based micro/ nanoparticles onto suitable supporting materials has been reported to be a promising method to reduce their aggregation and improve the operation process, thus improving their adsorption efficiency towards phosphate (Tesh & Scott, 2014; Zhang, Xu, et al., 2022) Many types of supporting polymer-based materials including polyacrylonitrile (PAN) nanofibers, poly(vinylidene fluoride) membranes, and porous carbons, have been employed to immobilize La-based micro/nanoparticles (Chen et al., 2018; He et al., 2015; Liu, Zong, et al., 2018) However, most of these materials suffer from various disadvantages such as tedious syn thetic steps (ex electrospinning, phase separation), low biocompati bility and high cost Therefore, loading La-based micro/nanoparticles onto suitable supporting materials using simple methods is highly desirable and of great significance Bacterial cellulose (BC) is considered to be the purest form of cel lulose that is free from hemicellulose, lignin and extractives It generally exists in the form of hydrogel with a three-dimensional (3D) network structure possessing excellent biocompatibility, biodegradability, excellent structure stability and high specific surface area (Klemm et al., 2011) These features combined with numerous functionalizable surface hydroxyl groups make BC a promising candidate for supporting various types of particles, such as gold nanoparticles, silver nanoparticles, and palladium nanoparticles (Kamal, Ahmad, Khan, & Asiri, 2019; Lv et al., 2018; Xie et al., 2019) However, combinations of BC with La-based micro/nanoparticles have been less reported, let alone their deploy ment as adsorbent for P removal and recovery In this study, we prepared a highly effective La(OH)3 nanoparticles (NPs)-based adsorbent for P removal by employing BC as the natural supporting material PEI grafted BC was first synthesized via a glutar aldehyde crosslinking reaction between the hydrogel groups of BC and the amine groups of PEI The introduced large number of amine groups has high affinity towards La(III), facilitating the subsequent in situ for mation of La(OH)3 NPs on the PEI-grafted BC (BPLa) The prepared BPLa adsorbents demonstrated fast adsorption kinetics and high removal ef ficiency Considering the simplicity of the fabrication method, the excellent phosphate removal performance and the environmental benign nature of the adsorbent, we believe the present material have great potential for practical removal and recovery of P butanol was renewed every 60 Compared with water, tert-butanol with a higher freezing point and a lower surface tension can lead to a decline in capillary force, thus reducing the damage to the gel network structure during the following freeze-drying process The obtained BC membrane (0.1 g) was then added to 500 mL of 0.5 % PEI aqueous so lution and stirred at room temperature for 300 After that, mL of 25 % glutaraldehyde solution was pipetted into the system and stirred for further 120 The PEI-modified BC hydrogel was then thoroughly washed with abundant Milli-Q water Afterward, the obtained BC hydrogel was soaked into 500 mL of lanthanum chloride solution with different initial concentrations (0.01 mol L− 1, 0.025 mol L− 1, 0.05 mol L− and 0.1 mol L− 1) at room temperature for 300 These four samples were named as BPLa-1, BPLa-2, BPLa-3 and BPLa-4, respec tively Subsequently, the BC hydrogels were immersed into 500 mL of sodium hydroxide solution (0.1 mol L− 1) for 300 After reaction, the La(OH)3 NPs-immobilized BC hydrogels were rinsed with plenty of water Finally, La(OH)3 NPs-immobilized BC aerogel membranes were obtained by freeze drying after solvent exchange of water by tertbutanol Materials and methods Qe = (C0 − Ce )V/m 2.3 The phosphate adsorption performance of the BPLa-X samples The adsorption capacity of BPLa-X was studied in batch with phos phate solution Briefly, 10 mg adsorbent was added into 20 mL of phosphate solutions with various concentrations and stirred (150 rpm) for 360 to ensure the adsorption equilibrium The adsorption isotherm experiments for BPLa-X were tested in different initial con centrations of phosphate solution ranging from to 350 mg P L− 1, and the adsorption kinetic experiments were studied at the time interval of 0.5–160 with an initial concentration of 30 mg P L− To examine the effect of pH on phosphate adsorption of BPLa samples, 10 mg adsorbent and 20 mL 100 mg P L− phosphate solution were shaken at 25 ◦ C for h with an initial pH between 3.0 and 10.0 To test the in fluence of coexisting ionic strength on phosphate removal of the sam ples, a mixture phosphate solution (150 mg P L− 1) was prepared with 200 mg L− coexisting anions by dissolving different salts of Na2SO4, NaCl, NaNO3, NaHCO3, Mg(NO3)2 and Ca(NO3)2 After reaching the adsorption equilibrium, the concentration of phosphate in the solution was quantitatively determined by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) Then the P loaded adsorbents were regenerated with M NaOH solution and desorbed continuously for 240 at room temperature Finally, the reusable adsorbent was continu ously cleaned with deionized water for the adsorbent to be reused in further experiment Each measurement was repeated three times in the experiment The adsorption capacity (per unit weight of adsorbent Qe (mg g− 1)) of the samples towards phosphate was calculated using the following expression: (1) where C0 (mg L− 1) is the initial concentration of phosphate; Ce (mg L− 1) is the equilibrium concentration of phosphate in solution; V (mL) is the solution volume and m (g) is the weight of the used adsorbent mass The adsorption thermodynamic analysis is usually evaluated by three important thermodynamic parameters, including the standard entropy change (ΔS◦ ), standard enthalpy change (ΔH◦ ) and standard free energy change (ΔG◦ ) ΔH◦ , ΔG◦ and ΔS◦ for BPLa-3 were calculated using following equations (Qu, Wei, et al., 2022; Qu et al., 2022), ( ) ◦ (2) ΔG = − RTln K0e 2.1 Materials BC was purchased from Beijing Guanlan Technology Co., Ltd PEI, glutaraldehyde and lanthanum hydroxide were received from Shanghai Aladdin Biochemical Technology Co., Ltd Sodium dihydrogen phos phate was bought from Shenggong Bioengineering Co., Ltd Lanthanum chloride was obtained from Shanghai McLean Biochemical Technology Co., Ltd tert-Butanol and sodium hydroxide were purchased from Xilong Science Co., Ltd Filter membrane (pore size, 0.22 μm) was purchased from Jinteng Experimental Equipment Co., Ltd ◦ ◦ 2.2 Synthesis of BPLa-X ( ) ΔS ΔH ln K0e = − R RT The exchange of water to tert-butanol was first conducted by placing BC hydrogel into tert-butanol and stirring for 300 Note that the tert- where K0e is the adsorption distribution coefficient and R represents the universal gas constant (8.314 J mol− K− 1) (3) L Tan et al Carbohydrate Polymers 298 (2022) 120135 2.4 Characterization Results and discussion Fourier transform infrared spectroscopy (FTIR) was performed on a nicolettm ISTM 50 (Thermo Fisher, USA) spectrometer X-ray diffraction (XRD) analysis was performed on Bruker D8 advanced diffractometer (Bruker, Germany) The specific surface area was measured by nitrogen adsorption isotherm method by quantachrome autosorb IQ (quantach rome, USA) surface analyzer Images of surface morphology were taken with Regulus 8220 scanning electron microscope (SEM) (Hitachi, Japan) at different magnifications Prior to SEM observation, the samples were sputtered with a layer of gold by E-1010 ion sputtering instrument (Hitachi, Japan) to improve the conductivity of the material X-ray photoelectron spectroscopy (XPS) spectra were identified by a Thermo Scientific K-Alpha spectrometer (USA) Thermogravimetric spectra were performed on a TGA 4000 thermogravimetric analyzer (PerkinElmer, USA) Mechanical properties were tested by a universal testing machine (CMT6503, MTS Industrial Systems Co., Ltd., China) with a speed of mm min− In this test, all the samples were cut into a rectangular shape, and at least five specimens were tested for each sample After adsorp tion, the solution is filtrated with 0.22 μm filter membrane, and the phosphate concentration in the solution was determined quantitatively by ICP-AES (Optima 2000dv, PerkinElmer) As introduced above, BC generally exists in the form of 3D network structure, which is composed of ultrafine nanofibers being around 10–1000 nm in length and 10–50 nm in diameter (Fig S1) (Wang, Tavakoli, & Tang, 2019) To introduce amine groups on the surface of these nanofibers, PEI was grafted onto BC by crosslinking via glutaral dehyde No obvious morphological change was observed for the PEIgrafted BC, as can be seen from Fig 1b The introduced amine groups with strong affinity for metal ions facilitate the subsequent in-situ growth of La(OH)3 NPs onto the PEI-grafted BC As is shown in Fig 1c–f, Labased NPs were homogeneously deposited onto the PEI-modified cel lulose nanofibers without obvious aggregation, which was also confirmed by the elemental analysis mapping (Figs 1h–j & S2) As can be seen, the morphology of the composite membrane remained the porous fibrous network of the native BC with different La contents In comparison, the synthesized La(OH)3 without BC support was aggre gated into large particles, which is not desirable for the further adsorption process towards P The structure changes during the treatment for preparing BPLa-X were characterized by FTIR spectroscopy (Fig 2a) It is obvious that the peak at 3340 cm− is attributed to the hydroxyl groups After chemically cross-linking with PEI, the peaks at 2908 and 2853 cm− were attributed to enhanced C–H stretching vibrations due to the large amount of -CH2 from PEI (Song, Liu, Zhu, & Li, 2019) The peak at 1569 Fig (a) Schematic diagram of BPLa synthesis SEM images of (b) BC/PEI, (c) BPLa-1, (d) BPLa-2, (e) BPLa-3, (f) BPLa-4 and (g) La(OH)3 (h–j) Elemental mapping of BPLa-3 L Tan et al Carbohydrate Polymers 298 (2022) 120135 Fig (a) FTIR spectra (b) XRD patterns (c) BET isotherms (d) Stress-strain curve of BPLa-3 in dry and wet conditions ăkila ă, Willfo ăr, & Xu, cm− is assigned to amine group (Zhang, Wang, Ma 2022) These results strongly indicate the successful grafting of PEI chains onto BC After the introduction of La(OH)3, the peak at 3340 cm− decreased dramatically, and the new absorption bands at 1495 cm− was assigned to the asymmetric stretching mode of the CO2− group, which is relevant to CO2 on the surface of La(OH)3 (SalavatiNiasari, Hosseinzadeh, & Davar, 2011) The changes of FTIR results indicated that the BPLa-X were successfully prepared We further employed X-ray diffraction (XRD) method to determine the crystalline structure of the as-synthesized La-based nanoparticles (Fig 2b) Five distinct peaks at 2θ = 16.2◦ , 27.6◦ , 39.8◦ , 47.8◦ and 55.2◦ corresponding to the (100), (101), (201), (300) and (112) plane of the cubic phase of La (OH)3 were observed for BPLa-3 (He et al., 2015; Zong et al., 2017) Moreover, from Fig 2b, we can conclude that La(OH)3 NPs synthesized according to the same procedures without using PEI-grafted BC as sup porting material displayed the same reflections with the La(OH)3 NPs immobilized on the BC nanofibers, indicating that the existence of PEIgrafted BC has no significant effect on the crystal phase of La(OH)3 Note: Three main peaks at 2θ = 14.8◦ , 16.8◦ and 22.5◦ assigned to dif fractions from the (110), (110), and (200) planes of cellulose I were observed for both pristine BC and PEG-grafted BC This could be explained by the fact that the PEI modification occurred on the surface of BC nanofibers, which would not destroy the crystalline structure of cellulose Generally, the porous structure and surface area of a porous adsor bent available for adsorption play crucial roles in determining its adsorption capacity Therefore, the N2 adsorption-desorption isotherms were measured to determine the specific surface area (SSA) of the assynthesized samples As can be seen from Fig 2c, typical type III hys teresis loops were observed for pristine BC, BP, BPLa-3 as well as La (OH)3 NPs, indicating the presence of mesoporous structures in these samples and the occurrence of capillary condensation Interestingly, the SSA of pristine BC, BP and La(OH)3 were calculated to be around 98.80, 111.95 and 6.94 m2 g− 1, while the BPLa-X samples had higher SSA of 117.47, 120.18, 123.90 and 128.19 m2 g− for BPLa-1, BPLa-2, BPLa-3 and BPLa-4 (Fig S3), respectively The stability of the adsorbents in water was also an important factor that should be considered for their practical application in phosphate removal from wastewater Fig 2d presented the stress-strain curve of BPLa-3 in dry and wet conditions The sample BPLa-3 at 50 % RH had a tensile strength and an elongation at break of 19.1 MPa and 3.3 % When the sample was wetted with water, it still presented excellent mechanical properties with tensile strength and an elongation at break of 12.1 MPa and 6.8 %, which is even comparable to synthetic polymer-based porous membrane (Ge et al., 2022; Issa, Al-Maadeed, Mrlík, & Luyt, 2016; Rianjanu, Kusu maatmaja, Suyono, & Triyana, 2018; Shi et al., 2012) The adsorption performance of the different samples towards P in water was investigated Fig 3a showed the comparison of the phosphate adsorption capacity of aggregated La(OH)3 powders, BPLa-X samples, pristine BC and BP As expected, pristine BC demonstrated no adsorption performance towards phosphate, which is mainly due to the absence of effective adsorption sites for phosphate on BC Compared to the pristine BC, BP showed slightly improved adsorption capacity for phosphate of around 16.5 ± 1.1 mg P g− This result is in line with previous study suggesting that PEI-modified ethyl cellulose can be employed for phosphate removal, with phosphate adsorption capacity of 15.53 mg P g− (Zong et al., 2021) It is worth noting that PEI, as a polymeric amine with a large amount of -NH and -NH2 groups, has a zero-potential point at a high pH value (Barick, Prasad Saha, Mitra, & Joshi, 2015) Thus, PEI is positively charged at acid, neutral and even weak basic surroundings, which is beneficial for the removal of many anion pollutants, for example, phosphate owing to the electrostatic interactions Compared with powder La(OH)3, pristine BC and BP, all the BPLa-X samples, namely BPLa-1, BPLa-2, BPLa-3 and BPLa-4, exhibited superior adsorption tendency for phosphate with adsorption capacities of 57 ± 2.2, 80 ± 2.5, 106 ± 4.5 and 108 ± 6.3 mg P g− 1, respectively The observed increase in the adsorption capacities of BPLa-X samples were mainly ascribed to the increase of the La content As displayed in Fig S4, the La contents of BPLa-1, BPLa-2, BPLa-3 and BPLa-4 were calculated to be 14.7 %, 29.5 %, 34.5 % and 35.4 % Considering the fact that com parable phosphate adsorption capacities were observed for BPLa-3 and BPLa-4, BPLa-3 was chosen for further studies including the adsorption L Tan et al Carbohydrate Polymers 298 (2022) 120135 Fig (a) Phosphate adsorption capacities of the prepared samples (b) Adsorption kinetic modeling of phosphate on BPLa-3 using pseudo first-order, pseudo second-order, and Avrami fractional-order models (initial phosphate con centrations: 30 mg P L− 1, adsorbent dosage: 0.5 g L− 1, pH: 6, temperature: 25 ◦ C) (c) Adsorption isotherms fitting of phosphate on BPLa-3 at different temperatures (Initial phosphate con centrations: 5–350 mg P L− 1, adsorbent dosage: 0.5 g L− 1, pH: 6, temperature: 10 ◦ C, 25 ◦ C, 40 ◦ C and contact time: h.) kinetics, recyclability, etc To better understand the adsorption process of the BPLa-3 towards phosphate in water, the pseudo-first-order adsorption model, pseudosecond-order adsorption model and Avrami fraction-order model were studied (Qu et al., 2022), and the kinetic parameters were shown in Fig 3b and Table S1 As demonstrated in Fig 3b, the adsorption amount of BPLa-3 for phosphate increased rapidly within 30 min, and reached the plateau after 75 Moreover, the serviceability of each model was assessed by using the adjusted determination coefficient (R2adj) and the standard deviation (SD) (Qu, Dong, et al., 2022) Generally, higher R2adj and lower SD indicate the better applicability of the corresponding ki netic model Fig 3b and Table S1 indicate that the adsorption process of the BPLa-3 towards phosphate obeys the pseudo-second-order kinetics, which is mainly controlled by chemical adsorption Furthermore, the Langmuir, Freundlich and Sips isotherm models were also investigated to study the adsorption mechanism From the adsorption isotherms and parameters shown in Fig 3c and Table S2, the phosphate adsorption process was better fitted with the Langmuir isotherm model with a higher correlation coefficient (R2adj = 0.9710) and lower SD (11.52) than other models at 25 ◦ C, suggesting that the adsorption behavior is monolayer adsorption process at room temperature According to the Langmuir equation, the maximum phosphate adsorption ability of BPLa3 was high to 125.5 mg P g− 1, which is 3.5 times higher than that of the prepared La(OH)3 (35 mg P g− 1) However, under other conditions, such as 10 ◦ C and 40 ◦ C, the phosphate adsorption process was better fitted with the Sips isotherm model, which is a combination of Langmuir and Freundlich models When the concentration of adsorbate is high, Sips model can predict the maximum unit adsorption of monolayer as Langmuir model; when the concentration of adsorbate is low, Sips model can describe the adsorption behavior of adsorbent as Freundlich model (Zhang, Qu, et al., 2022) In addition, the thermodynamics were also analyzed to study the phosphate adsorption process As shown in Table S3, ΔG◦ and ΔH◦ are negative at all temperatures, indicating that the phosphate adsorption process of BPLa-3 is spontaneous and exothermic In the studied temperature range, the amplitude of ΔG◦ value decreases with the increase of temperature, which may correspond to the decrease of spontaneity at the elevated temperature In addition, the value of ΔG◦ greater than − 20 kJ mol− and less than − 80 kJ mol− demonstrated that the adsorption process includes both physical adsorption and chemical adsorption (Ahmed, Okoye, Hummadi, & Hameed, 2019) The value of ΔS◦ is positive, indicating that the randomness of the solid-liquid interface increases during the adsorption process Notably, BPLa-3 presented a high adsorption capacity (127 mg P g− 1) for P (glyphosate) (Fig S5) The excellent adsorption perfor mance of BPLa-3 for P removal is mainly because of the porous fibrous structure and the homogeneously distributed La(OH)3 NPs on the sur face of BC nanofibers The pH value is an important factor influencing the adsorption performance of the adsorbent (Qu, Wu, et al., 2022) As is shown in Fig 4a, the adsorption capacity could reach up to 116.6 mg P L− at pH and then decreased with increasing the pH value from to 10 In this pH range, H2PO−4 and HPO2− are the dominant species in the solutions (Zong et al., 2018), and the zeta potential of the adsorbent decreased dramatically with increasing the pH value (Fig S6) There fore, the decrease in the adsorption capacity is probably due to the weakening of the electrostatic attraction between the adsorbent, H2PO4− and HPO2− In addition, many other anions generally co-exist with phosphate in practical water and/or wastewater may also influence the adsorption performance Thus, a desirable adsorbent should possess high adsorp tion selectivity towards phosphate In this work, to evaluate the adsorption selectivity towards phosphate, the adsorption studies of BPLa-3 were conducted in the presence of various competing anions including chloride, carbonate, sulfate, nitrate, and mixtures of these anions According to the results shown in Fig 4b, it can be concluded that these competing ions have a negligible effect on the adsorption selectivity for phosphate of BPLa-3 This result is in good agreement with previous studies on phosphate adsorption by La-based adsorbents (Zhang, Xu, et al., 2022; Zong et al., 2018) The reusability of an adsorbent is an important index in assessing its practical applicability In this work, BPLa-3 was firstly immersed in phosphate solution with the initial concentration of 150 mg P L− After being immersed for 160 min, BPLa-3 was picked up, squeezed and then immersed in M NaOH solution for 240 After that, BPLa-3 was separated from NaOH solution and washed with deionized water until neutral pH The regenerated BPLa-3 was then employed for the subse quent cycle of adsorption As seen in Fig 4c, after four consecutive cy cles of adsorption-desorption, the adsorption capacity of phosphate by BPLa-3 was maintained at 101.7 mg P g− 1, which is comparable or Fig Effect of (a) pH, (b) anions and (c) adsorption-desorption cycles (c) on the adsorption performance of BPLa-3 Carbohydrate Polymers 298 (2022) 120135 L Tan et al superior to many other La-based adsorbents (Table 1) A slight decrease in the adsorption capacity should be mainly ascribed to the inevitable lanthanum leaching (Fig S7) Compared to many other La-based adsorbents previously reported for phosphate removal, BPLa-3 showed much higher adsorption capacity and faster adsorption kinetics (Table 1) For instance, Chen et al re ported the in-situ preparation of La(OH)3-poly(vinylidene fluoride) composite filtration membrane for phosphate removal Although a high permeability was achieved, the membrane had an adsorption capacity of only 13.86 mg P g− 1, which is much lower than that of BPLa-3 The difference in the adsorption performance between BPLa samples and these sorbents and membranes can be explained from the two main factors, the La content and the specific surface area Obviously, higher La content can provide more adsorption sites for phosphate, enabling the sorbents with higher adsorption capacity As for the as-prepared BPLa samples, the La content could reach up to around 35 % Addi tionally, the introduced amine groups also work as phosphate adsorp tion sites, also contributing to the excellent adsorption performance of BPLa samples The microstructure of the sorbent is also an important factor that determines their adsorption performance In this work, the insitu synthesis of La(OH)3 NPs on the nanofibers of porous BC efficiently prevented the aggregation of these NPs, thus providing more exposed phosphate adsorption sites Note: Studies revealed that lanthanum hy droxide generally can offer more adsorption sites, for example, surface hydroxyl groups, than lanthanum oxide Thus, the BPLa-X samples also possess higher adsorption capacity than that of many La-based adsor bents (Table 1) In order to probe the possible adsorption mechanism of phosphate onto BPLa adsorbent, a series of characterization experiments were carried out in this study As shown in Fig 5a, the O-P-O bond bending − vibration in PO3− groups can be observed at 608 and 534 cm , indi cating that phosphate is successfully adsorbed on BPLa-3 It also can be seen that after phosphate adsorption, the stretching vibration peak of La–O at 845 cm− decreased, which means that La–O bond partici pates in the adsorption with phosphate (Li et al., 2021) Moreover, XPS spectra were also performed to explore the adsorption mechanism of phosphate by BPLa-3 (Qu, Yuan, et al., 2022) The wide scan XPS spectra of BPLa-3 before and after phosphate adsorption indicated the presence of C, O, La and P elements (shown in Fig 5b) The presence of a distinguished peak centered at ~133.4 eV indicated the appearance of phosphorus after the phosphate adsorption The P 2p spectrum from standard samples are located at ~134.0 eV and ~0.6 eV to lower energy levels after phosphate adsorption, indicating a strong affinity between phosphate and BPLa-3 (Liu et al., 2022) As shown in Fig 5c, the representative satellite peaks of La 3d5/2 and La 3d3/2 in BPLa-3 are concentrated at ~835.8 eV and ~851.8 eV, respectively The shift of the peak to higher energy is usually observed in La-based compounds, which can be explained by the transfer of elec trons from the valence band of the ligand atom (Lu et al., 2021) Obvi ously, the absorption peaks of La 3d5/2 and La 3d3/2 shift to higher binding energies after phosphate adsorption, indicating the formation of new La-O-P complexes In addition, the binding types of O elements on BPLa-3 surface before and after phosphate adsorption were analyzed by high-resolution XPS scanning As shown in Fig 5d–e, the O 1s spectrum is divided into three overlapping peaks, corresponding to C–O (~532.8 eV), La-OH (~531.4 eV) and La–O (~529.9 eV) derived from the BPLa adsorbent, respectively After phosphate adsorption, the area ratio of the peak attributed to the percentage of La–O increased from 6.06 % to 7.24 %, while the relative area ratio of the peak of La-OH decreased from 47.42 % to 20.41 %, which confirmed that the hydroxyl groups on the surface of BPLa adsorbent played a major role in phosphate adsorption, thus leading to the substitution of hydroxyl groups by phosphate during the adsorption process (Zong et al., 2018) The XRD patterns of BPLa-3 before and after phosphate adsorption were recorded in Fig 5f Compared with the original BPLa-3, it is obvious that the range, in tensity and properties of the peaks are greatly different from those of the original adsorbent after phosphate adsorption Additionally, the char acteristic diffraction peaks at 28.7◦ , 31.2◦ and 42.0◦ indicated that the adsorption of phosphate by BPLa sample could result in the formation of LaPO4 via a ligand exchange mechanism between P ions and La-OH (Huang, Zhu, et al., 2014) Conclusions In this work, a high-efficient adsorbent for phosphate removal was facilely constructed by in-situ synthesizing La(OH)3 NPs on PEI-modified BC The resultant porous fibrous sample BPLa-3 demonstrated high adsorption capacity of 125.5 mg P g− 1, fast adsorption kinetics of ~75 and high adsorption selectivity towards phosphate in the presence of various anions at room temperature Moreover, BPLa-3 can be easily regenerated by simple immersion in NaOH solution, and a high adsorption capacity of 101.7 mg P g− was still maintained even after four consecutive cycles of adsorption-desorption Considering these merits of such an adsorbent, BPLa is believed to be a promising Table Comparison of phosphate adsorption capacities of different La-based materials Adsorbents Equilibrium time (min) Qm (mg P g− 1) Qm (mg P g− content) La/Al pillared clays La/carbon fiber 300 13.02 120 La-silica spheres La-vermiculites La/CNC La-zeolite La) (La Specific surface area (m2g) Average pore diameter (nm) Pore volume (cm3/g) Ref – – – – 29.44 155.11 (18.98 %) – – – 1440 2880 180 – 47.89 79.6 47.28 17.2 213.41 (22.44 %) 252.54 (31.52 %) 256.82 (18.41 %) 227.81 (7.55 %) 420.38 39.1 136 52.75 2.46 20.74 6.71 5.78 0.23 0.17 0.36 0.076 La/Fe3O4 240 45.45 – – – – La/lignin La/PVDF La/chitosan La/Fe3O4/lignin La-iron oxide La/biochar La-hydrogel La/graphene La/BC membrane 60 200 10 360 180 480 120 1000 75 65.79 13.86 57.84 60.36 88.6 37.37 105.72 76.85 125.5 229.71 (28.64 %) 256.6 (5.4 %) 98.60 (58.66 %) – – – 335.62 (31.5 %) – 363.35 (34.54 %) 85.78 – 12.47 208 131.92 – 11.32 158.9 123.90 – – – – – – 10.83 4.5 0.31 0.44 – – 0.46 – – 0.03 – 1.004 (Tian, Jiang, Ning, & Su, 2009) (Liu, Zhou, Chen, Zhang, & Chang, 2013) (Huang et al., 2014) (Huang et al., 2014) (Zheng et al., 2016) (He, Lin, Dong, & Wang, 2017) (Liu, Chen, Wang, Zheng, & Yang, 2018) (Zong et al., 2018) (Chen et al., 2018) (Liu et al., 2020) (Li, Li, et al., 2021) (Lu et al., 2021) (Liu et al., 2022) (Zhou et al., 2022) (Wang et al., 2022) This work L Tan et al Carbohydrate Polymers 298 (2022) 120135 Fig (a) FTIR analysis of the BPLa-3 before or after phosphate adsorption (b) XPS survey scan of BPLa-3 before and after phosphate adsorption (c) La spectra before and after phosphate adsorption (d) O1s spectra of pristine BPLa-3 (e) O1s spectra of BPLa-3 after phosphate adsorption (f) XRD analysis of the BPLa-3 before or after phosphate adsorption candidate for phosphate removal in practical applications org/10.1016/j.carbpol.2022.120135 CRediT authorship contribution statement References Liping Tan: Conceptualization, Methodology, Writing – original draft Weihua Zhang: Conceptualization, 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FTIR analysis of the BPLa-3 before or after phosphate adsorption (b) XPS survey scan of BPLa-3 before and after phosphate adsorption (c) La spectra before and after phosphate adsorption (d) O1s... BPLa-3 (e) O1s spectra of BPLa-3 after phosphate adsorption (f) XRD analysis of the BPLa-3 before or after phosphate adsorption candidate for phosphate removal in practical applications org/10.1016/j.carbpol.2022.120135