Structure models of sepiolite group minerals: sepiolite (a) and palygorskite (b) (Bailey SW 1980, Ref. [2])

Contexts in source publication

Context 1

... structure, and physicalchemical properties of typical nano-geomaterials. Moreover, the various activation and modification strategies to increase their performance in water treatment were also provided. Finally, the application of nano-geomaterials in the removal of aqueous contaminants such as heavy metals and organic pollutants was summarized. (Fig. 1a) [1]. Besides, palygorskite (PAL or PGS) also called attapulgite (ATP) also belongs to the family of sepiolite. It is very similar with sepiolite both on composition and structure and has similar performance with sepiolite [2]. Its crystal structure was shown as Fig. 1b. The structure of sepiolite is similar to those of other 2:1 ...

Context 2

... contaminants such as heavy metals and organic pollutants was summarized. (Fig. 1a) [1]. Besides, palygorskite (PAL or PGS) also called attapulgite (ATP) also belongs to the family of sepiolite. It is very similar with sepiolite both on composition and structure and has similar performance with sepiolite [2]. Its crystal structure was shown as Fig. 1b. The structure of sepiolite is similar to those of other 2:1 trioctahedral silicates, such as talc. Differently, it has discontinuities and inversion of the silica sheets, which give rise to structural tunnels and blocks. In the inner blocks, all corners of the silica tetrahedral are connected to adjacent blocks; in the outer blocks, ...

Context 3

... shown in Fig. 10, kaolinite belongs to the same kaolinite group with halloysite. Its structure is layered with interlayer space and the layers may be electrically neutral or charged ...

Context 4

... instance, the maximum adsorption capacity of HNTs for methylene blue was 84.32 mg g À1 , and the dye adsorption equilibrium was rapidly attained after 30 min of contact time [27]. Figure 11 further showed the adsorption of methyl violet (MV) and neutral red (NR) from aqueous solutions by using adsorbent of HNTs [28,29]. The adsorbent exhibited rapid adsorption rate and high adsorption capacity of 113.64 mg g À1 for MV and 65.45 mg g À1 for NR in 318 K. ...

Context 5

... and low budget compared with modification by surface-active agents and oxides because acid is relatively inexpensive and recyclable. For instance, sulfuric acid activation at certain temperature can enlarge the lumen of HNTs, and the specific surface area of the acid treated HNTs increased over six times, from 40 m 2 g À1 to 250 m 2 g À1 (see Fig. 12) ...

Context 6

... trimethoxysilane (KH-792)-modified HNTs exhibited a rapid adsorption rate for Cr (VI) and approached 95% of the maximum adsorption capacity within 5 min [42]. Moreover, polyethyleneimine (PEI) onto APTES-HNTs exhibited high isoelectric point and excellent ability for Cr (VI) reduction and immobilization from wastewater (see Fig. 13) [43]. The Cr (VI) uptake capacity was about 64 times higher than that of the original HNTs, and the maximum equilibrium removal capacity was found to be 102.5 mg g À1 at 328 K. The increase of surface positive charge was responsible to the enhancement of the removal efficiency for heavy ...

Context 7

... natural biopolymers such as chitosan, alginate, cellulose, polylactide, guar gum, etc. are also good alternative for the medication of HNTs. As shown in Fig. 14, chitosan (CTS) was assembled onto halloysite, and horseradish peroxidase (HRP) was further immobilized through cross-linking by glutaraldehyde [44]. A new porous bead by immobilizing alginate on halloysite nanotubes (Alg-HNTs) was also prepared [45]. The above two materials exhibited overall high removal efficiency and removal rate ...

Context 8

... to halloysite, kaolinite can be also modified by organic functional groups. Polyacrylic acid (PAA) brushes were then successfully decorated on the surface of kaolinite (KLN) via a facile "one-step" manner ( Fig. 15) [47]. It exhibited an enhanced adsorption and stability performance than raw kaolinite. The adsorption amount of Cu 2+ can reach 32.45 mg g À1 . In addition, the regeneration experiment showed that the PAAg-KLN could still keep a satisfactory adsorption capacity (> 65%) by being reused for six consecutive ...

Context 9

... Ag, and CeO 2 [48,49]. HNT-supported Ag nanoparticles (Ag/HNTs) were synthesized for catalytic reduction of 4-nitrophenol (4-NP), which exhibited good catalytic activity for the reduction of aromatic nitro compounds to the corresponding amino derivatives [50]. Besides, Ag/HNTs could be used for photocatalytic decomposition of methylene blue (see Fig. 16), which exhibited good catalytic activity and high removal capacity for methylene blue [51]. Within 60 min, nearly 90% of MB had been decomposed photocatalytically by the HNTs/ AgNP ...

Context 10

... electric conductivity and the interaction between metal ions and HNTs can be effectively improved by coating carbon on the surface of HNTs. In addition, metal Fig. 15 Scheme of preparation of PAA-g-KLN composite [47] species such as Ti 4+ , Fe 3+ , Ni 2+ , and Co 2+ can be easily anchored on the oxygencontaining organic groups of carbonaceous material surface to form metal oxideanchored adsorbent material. As shown in Fig. 17, the carbonization process was conducted using sucrose in the presence of ...

Context 11

... be effectively improved by coating carbon on the surface of HNTs. In addition, metal Fig. 15 Scheme of preparation of PAA-g-KLN composite [47] species such as Ti 4+ , Fe 3+ , Ni 2+ , and Co 2+ can be easily anchored on the oxygencontaining organic groups of carbonaceous material surface to form metal oxideanchored adsorbent material. As shown in Fig. 17, the carbonization process was conducted using sucrose in the presence of sulfuric acid [52]. The carbon-coated HNTs (CCH) were then deposited by ZnO-or TiO 2 -nanosized metal oxide (MO) to produce MO/CCH nanocomposites. The photocatalytic performance of MO/CCH for the methylene blue dye degradation was improved due to the increased ...

Context 12

... of an external magnetic field and regenerated by simple calcinations. Additionally, a novel "dumbbell-like" magnetic Fe3O4/HNT was prepared for Cr (VI) reduction and immobilization, in which oxygen-containing organic group was grafted on the surface of natural HNTs (HNTs@C)and Fe3O4 nanospheres were selectively aggregatd on the modified HNTs (see Fig. 18). [53]. The maximum adsorption capacity was 132 mg L À1 at 303 K, which is about 100 times higher than that of unmodified HNTs. Due to the reduction of Fe 3 O 4 and electron-donor effect of oxygen-containing organic groups, Cr (VI) ions were easily reduced into low toxicity Cr (III) and then adsorbed onto the surface of adsorbents. In ...

Context 13

... [53]. The maximum adsorption capacity was 132 mg L À1 at 303 K, which is about 100 times higher than that of unmodified HNTs. Due to the reduction of Fe 3 O 4 and electron-donor effect of oxygen-containing organic groups, Cr (VI) ions were easily reduced into low toxicity Cr (III) and then adsorbed onto the surface of adsorbents. In addition, Fig. 16 Illustration of synthesis of HNT supported AgNPs [51] appreciable magnetization was observed due to the aggregation of magnetite nanoparticles, which make adsorbent facility separated from aqueous solutions after Cr pollution ...

Context 14

... and heavy metal ions, is another strategy for the application of halloysite in water treatment. NaA zeolite generated from natural halloysite has a single phase and highly crystalline, which exhibited a much higher performance for NH 4 + removal than the reported adsorbents with a maximum adsorption capacity of 44.3 mg g À1 [54]. As shown in Fig. 19, by mixing the HNT-derived zeolite with graphene oxide nanosheets, a spherical zeolite/reduced graphene oxide composite can be obtained [55]. Although the tubular structure of HNTs was destroyed and a cubic or spherical zeolite was generated, the composite showed an effective adsorption capacity of 53.3 mg g À1 for methylene blue and ...

Context 15

... structure with unique properties such as adsorption capacity, anion exchange capacity, and mobility of interlayer anions and water molecules. Moreover, LDHs can form stable and homogeneous mixed oxides with spinel-type structure after calcination. During the structure reconstruction process, anionic pollutants could be uptake when exposed to Fig. 19 Schematic showing the synthesis of zeolite/rGO composite and the removal of cationic dyes [55] water and carbon dioxide. These LDHs and calcined LDHs have been widely studied as adsorbents for various pollutants or as catalysts and catalyst ...

Context 16

... application of LDH powder as sorbents shows some drawbacks, such as the formation of aggregates and difficulties in subsequent separation, regeneration, and recycling processes. Various chemical modifications of layered double hydroxides have been developed to fabricate LDH-based adsorbents with excellent sorption behaviors (see Fig. 21) ...