Project 3

STRICT HANDOUT — Nano Ni–Histidine MOF-like Framework (Hydrothermal)

Nano-target protocol Hydrothermal For XRD · FTIR · BET · SEM
Material name (reporting): Ni–L-histidine coordination framework (bio-MOF-like coordination polymer)

Safety (NON-NEGOTIABLE)

• Nickel salts: toxic/sensitizer. Wear gloves, lab coat, mask. Avoid skin contact.
• Ammonia fumes: handle in fume hood / strong ventilation.
• Autoclave: Fill ≤ 80% liner volume. Cool fully before opening. Never open hot/pressurized.
• Waste: Collect all Ni-containing liquids in labeled heavy-metal waste. Do not pour to sink.

Gloves Mask Fume hood Waste bottle labeled

1) Chemicals (from stock)

Metal node (preferred)

• Nickel(II) nitrate hexahydrate Ni(NO₃)₂·6H₂O

Alternative: Nickel(II) chloride works but nitrate gives cleaner crystallization.

Linker + nano-control

• L-histidine hydrochloride (L-His·HCl)
• PEG or PVP (optional but recommended for nano)

pH adjuster: aqueous ammonia · Solvent: DI water

2) Recommended nano batch recipe (1 mmol Ni scale)

Stoichiometry: Ni : His = 1 : 2   (good starting point for stable networks)

Reagent	Amount	Purpose / Note
Ni(NO₃)₂·6H₂O	0.291 g (1.00 mmol)	Metal node (Ni²⁺)
L-Histidine·HCl	0.419 g (2.00 mmol)	Multidentate ligand (builds framework)
DI water	30 mL total	Reaction medium
PEG or PVP (nano-control)	0.10 g	Limits crystal growth → smaller particles
Aqueous ammonia	Dropwise to pH 6.5–6.8	Critical: avoid Ni(OH)₂ impurity by not overshooting pH

Critical control point: Final pH must be 6.5–6.8.
If pH ≥ 7.2 → high risk of Ni(OH)₂ impurity (bad XRD, poor porosity).

3) Step-by-step procedure (STRICT)

A) Prepare clear solutions

1. Label beakers: “Ni solution”, “Ligand solution”.
2. Dissolve 0.291 g Ni(NO₃)₂·6H₂O in 15 mL DI water → stir until clear.
3. Dissolve 0.419 g L-His·HCl in 15 mL DI water → stir until clear.
4. Nano step: Add 0.10 g PEG or PVP into the ligand solution and dissolve completely.

B) Controlled mixing + pH set (decides success)

1. Start stirring the Ni solution (moderate speed).
2. Add ligand solution slowly over 2–3 minutes into Ni solution (steady stream / dropwise).
3. Measure pH using fresh pH paper.
4. Add aqueous ammonia dropwise while stirring until pH reaches 6.5–6.8. STOP.
5. Continue stirring for 30 minutes (aging).

Expected observation: mixture may become slightly turbid; that is acceptable.
Reject sign: heavy bright-green hydroxide-like precipitate immediately after ammonia addition.

C) Hydrothermal treatment

1. Transfer mixture into Teflon liner. Ensure fill level ≤ 80%.
2. Seal autoclave properly (gasket seated; tighten evenly).
3. Heat in oven at 140 °C for 6 hours (nano-favoring condition).
4. Allow natural cooling to room temperature before opening.

D) Recovery and BET-grade washing (MANDATORY)

1. Collect solid by centrifugation or filtration.
2. Wash 1: 30 mL DI water → stir/sonicate 2 min → separate.
3. Wash 2: 30 mL DI water → repeat.
4. Wash 3: 20 mL 2-propanol (or ethanol) → separate.
5. Wash 4: 20 mL 2-propanol (or ethanol) → repeat.
6. Dry at 60 °C for 6–8 hours.

Label vial exactly as:
Ni–His HT, 140C-6h, pH 6.7, PEG/PVP yes/no, date, batch #

4) Nano assurance knobs (use if particles are too big)

• Keep PEG/PVP at 0.10 g (do not skip).
• Lower concentration: double solvent (60 mL total) keeping same mmol ratios.
• Shorter time: 140 °C for 4–5 h (trial) if crystals grow too large.
• Do NOT increase pH to “speed up precipitation”—it creates hydroxide impurity.

5) Characterization checklist (do exactly)

XRD

• Gentle grind (no overgrinding).
• Scan: 5–70° (2θ), step 0.02°.
• Compare batches for crystallinity vs nano size (peak broadening).

FTIR

• ATR or KBr pellet.
• Look for shifts in COO⁻ stretches and histidine ring/N–H region.
• Absence of “free” acid behavior supports coordination.

BET (critical)

• Only well-washed sample (IPA/EtOH wash mandatory).
• Degas: 100–120 °C, vacuum, 6–12 h.
• Record: mass, degas conditions, isotherm.

SEM

• Carbon tape mount; sputter coat if charging.
• Capture images at 5k, 20k, 50k magnification.
• Report morphology + size distribution (nano vs micro).

6) Pass/Fail decision (before proceeding)

PASS: uniform powder; no slimy gel; no obvious salt crystals; stable after washing/drying.

FAIL / REPEAT: heavy gelatinous mass, strong hydroxide-like precipitate, or pH exceeded 7.2.
Fix: repeat with pH max 6.8 and slower ammonia addition.

Internal note (for reporting): This is best described as a bio-MOF-like coordination framework. If BET is low, it may be a dense coordination polymer; optimize via better solvent exchange and controlled pH.