**3.1 Delamination of layered zeolite under mild conditions**

The conventional delamination process includes the swelling process and a subsequent ultrasound treatment in alkaline solution with the typical pH value of ~13, which causes severe dissolution of the intralayer structures [30, 31]. Moreover, the mesoporous phase formed form dissolved silica species in swelling process, like MCM-41, may also contribute to the high surface area, which could give cheating information for the success delamination. Zones and Katz reported a delaminated MWW zeolite synthesized under mild condition, where a solution of tetrabutylammonium fluoride and chloride surfactants with a pH value of 9 was used (**Figure 6**) [65]. The fluoride ion could form a strong interaction with Si atoms, while the chloride ions would attack Al atoms in the delamination process. High solid yield of ~90% was obtained under the mild condition compared to the yield of ~75% under classical alkaline condition with the same treatment temperature and duration. The successful delamination was strongly evidenced by the loss of interlayer 10R pores, characterized by the decrease of the N2 uptake in the relative pressure of 10<sup>−</sup><sup>7</sup> < *p/p0* < 10<sup>−</sup><sup>4</sup> . The absence of Q2 signals and the sharper Q4 resonance bands in the 29Si NMR spectrum of delaminated UCB-1 material strongly indicated that the intralayer structure was well-preserved under the mild condition. However, a nonaqueous fluoride/chloride solution was needed in the delamination of the PREFER lamellar zeolite, and dimethylformamide was proved to be a suitable solvent in producing the delaminated UCB-2 material [66].

**Figure 6.** *Mild delamination of MWW-layered zeolite with the assistance of F<sup>−</sup> and Cl<sup>−</sup> ions.*

A more simple and mild delamination strategy without surfactant molecules and sonication was also proposed by Zones and Katz via the isomorphous substitution of Al for B in the B-containing MWW zeolite using aqueous Al(NO3)3 solution (**Figure 7**) [67]. The presence of neutral amine SDA and the careful control of temperature were proved to be critical for the success of this one-step delamination process. The obtained delaminated Al-containing ERB-1-del showed a similar morphology of single thin layers as the conventional delaminated ITQ-2 material and showed higher activity in Friedel-Crafts acylation reactions involving bulky substrates compared to 3D ERB-1C zeolite, due to the enhanced external surface area (133 *vs* 53 m2 /g). An all-silica analog of ERB-1-del can be obtained by treating ERB-1 lamellar precursor with warm Zn(NO3)2 solution with a pH value of ~1 [68]. However, the one-step mild delamination strategy is now restricted to ERB-1 lamellar precursor and has its limitations in the general application.
