I suggest Ball milling for bulk preparation of nanomaterials. You can prepare in large scale with uniform size. But the stress induced due to milling will affect the properties, but not in all casses

The best are molecule (polymers, peptides, metals) self-assembly methods in water as a solvent and hydrophobicity as molecule assembly driving force. Nanoparticles are stable and technique is environmentally friendly and easy to scale up. You just add reagents to the chemical reactor and one can have up to 100g per liter reactor volume (www.nanovelos.com).

They are several processes. However you can consider 2 strategies : top-down (for example the ball miling, but you have to be carefull with the agglomeration of the particles and pollution issues) and bottom-up (wet chemical processes, aerosol pyrolysis,... ).

The parameters are dependant of the processes of course. However, you have to keep in mind that the more difficult is to obtain non agglomerated, or at least well dispersed, nanoparticles.

Ball milling is the technique. Planetary ball mill (fritsch pulverisette) , attritor mill, spex mill, tumbler mill all the high energy ball mill and are commercialized. Even suing globe box facility will provide the same benefit.

If you use a wet chemistry method, don´t forget drying is an important bottleneck. If you unproperly dry a suspension, your nanoparticles may be microparticles. And this is also a hot topic for discussion, because freeze dry is most of the times the best strategy, but it´s a bit expensive.

Thank you all for your inputs. I have the following concerns :

1. Ball milling may be the best scaled up method. However, we wiuldn't get well-dispersed nanoparticles. There is high chance of polydispersity.

2. Wet chemistry methods are great however, drying is definitely a concern. Drying lead to agglomeration. Nanoparticles, due to high surface energy tend to agglomerate. Though freeze drying is the best option, we often find agglomeration in case of FD too. Then we have to use cryo/lyo protectants. 

3. The most important question is whether the properties remain intact when we go from lab scale to industrial scale - How much compromise can we do?

I would consider looking at aerosol based techniques for mass fabrication

These techniques do not need drying like wet techniques, but do not reuire crushing and milling either.

They also can be size and property specific.

Scale-up only requires larger furnaces and higher gas flows etc.

Here are some examples

Title: Size-selected nanocrystals of III-V semiconductor materials by the aerotaxy method

Author(s): DEPPERT, K; MAGNUSSON, MH; SAMUELSON, L; et al.

Source: JOURNAL OF AEROSOL SCIENCE Volume: 29 Issue: 5-6 Pages: 737-748 Published: JUN-JUL 1998

Feasibility study of nanoparticle synthesis from powders of compounds with incongruent sublimation behavior by the evaporation/condensation method

Author(s): DEPPERT, K; NIELSCH, K; MAGNUSSON, MH; et al.

Source: NANOSTRUCTURED MATERIALS Volume: 10 Issue: 4 Pages: 565-573 Published: MAY 1998

Times Cited: 3

Single-crystalline tungsten nanoparticles produced by thermal decomposition of tungsten hexacarbonyl

Author(s): MAGNUSSON, MH; DEPPERT, K; MALM, JO

Source: JOURNAL OF MATERIALS RESEARCH Volume: 15 Issue: 7 Pages: 1564-1569 Published: JUL 2000

I follow Tomasz Ciach answer.

This question is formulated too broadly. Unfortunately, the development of industrial technology for production of nanoparticles is needed to select a particular material and pre-conduct studies of all stages of the preparation of nanoparticles in the laboratory. Experience shows that, as a rule,  the development of industrial technology such production requires much more time.

If we produce nanoparticles in water by self assembly, we can dry it in the spray dryer. Nanoparticles reassemble few minutes after adding water. In most of the cases we use nanoparticles in some medium, most frequently solvent, and the best solvent is water. The best sources of inspiration are nanoparticles designed by the Great Engineer (or nature), He uses molecular selfassembly approach. Those are the most efficient nanorobots ever exist (ribosome, 20nm dia.), and everybody have seen and apply its products…

Sonal you asked a very nice question. However it is very difficult to generalize the synthesis processes.

If you look at metal oxide nanoparticles, they are normally prepared commercially by spraying using a flame.

Quantum dots that are used in biology are normally done by precipitation. Metal nanoparticles like silver, the ones used for antimicrobial applications are also precipitated in aqueous media.

High purity metal nanoparticles are prepared by gas phase processes (check nanophase, a very old company.... probably a pioneer). So, as you see, there are many ways of making the nanoparticles. We have discussed this aspect in a lot of details in our textbooks published in 2008. You may like to take a look:

(i) Introduction to NanoScience, (CRC Press of Taylor and Francis Group LLC), May 2008, 856pp, ISBN-13: 9781420048056

G. Louis Hornyak, Joydeep Dutta, Harry F. Tibbals and Anil K. Rao

(ii) Fundamentals of Nanotechnology, (CRC Press of Taylor and Francis Group LLC), December 2008, 832pp, ISBN-13: 9781420048032

G. Louis Hornyak, John J. Moore, Harry F. Tibbals and Joydeep Dutta

Thank you Dr. Dutta. I am just interested in how many of these processes can be scaled up for high production of nanoparticles? And if/when scaled up, did the properties still remain intact as the lab scale and if they differ, then to what extent?

I have helped scale up a couple of synthesis processes using precipitation. The particle sizes were definitely not that narrow as you would get in lab but its not too bad. Usually 10% variation, but for most practical applications that's fine

Three methods are adviced.

1) Ball milling. As one of most popular method in top-down methods, ball milling is easier and convenientfor conmmercialization.

2) wet-chemical method. You can use microfluidic System to make them continuous and scaled.

3) spay drying. It's suitable to core-shell structure nano or micro-particles.

Thank you very much for your inputs.

Organic medium assisted synthesis using Poly ethylene glycol or ethanol may help you for large scale synthesis.

If you are looking for a simple, quick and relatively green method you may consult two attached publications from our research team. You can generate naanoparticles of relatively uniform size within one hour. Only non-green aspect of these methods is use of electrical energy (for autoclaving). I believe, with this protocol we can generate nanoparticles of all precious metals at commercial scale. Mannitol seems to be superior in certain aspects. As nanoparticles are generated under sterile conditions,

I agree with Dr P. Pardha-Saradhi answer.

For wet-chemical methods, one can use chemical engineering methodology and concepts for scaling up nanoparticle precipitation. Please  read our recent paper for details

Ouar et al., Magnetic nanowire synthesis: A chemical engineering approach ... American Institute of Chemical Engineers AIChE J, 2014.

Its very tough to generalize a particular method for synthesis of nano-particles on a larger scale. For example, I work on hybrid nano-particles using organic dyes and I am able to get sufficiently good yield on a large scale using Sol-Gel method. Have to be specific with respect to required nano-particles. 

It depends upon the materials and what micro-structure is expected in the product.

Generally chemical route is cheaper and can produce in bulk. like sol gel methods..

In my opinion bottom up wet chemical methods specially hydrothermal or solvothermal  methods are good options for scaled up synthesis of nano-materials. We can even use continuous hydrothermal flow synthesis (CHFS), there are plenty literature on CHFC. 

see Shyman Project 

e.g.

https://www.linkedin.com/groups/EU-project-continuous-nanparticle-production-7463295.S.5890182169615171587?trk=groups_items_see_more-0-b-ttl

Nanoparticles synthesis has been explained by so many techniques such as Physical, Chemical and biological routes. Among them chemical routes are more commercialized for its simplicity, possibility of wide range of nanoparticles synthesis and controlled growth rate. Some of the chemical route for the synthesis of nanoparticles are Chemical Reduction method, Electrochemical Reduction, Sol-Gel process, Co-precipitation method, Solvo-thermal method, Micro-emulsion method, Reverse micelle technique, Thermal decomposition, Photochemical synthesis, Metal vapor synthesis, Sonochemical method, Template Synthesis, Spray pyrolysis, Hydrothermal method, Radiation-Assisted Reduction, Solvated metal atom dispersion, Solution combustion synthesis, Chemical vapor synthesis.

             Chemical reduction method for metal nanoparticles synthesis and Co-precipitation method, Sol-Gel process for the synthesis of metal oxide, complex metal oxide nanoparticles are suitable for better commercialization. However, precise particles size, shape, size distribution, solubility in particular solvents in future applications, stability, to avoid by products for purity are important in nanoparticles synthesis. To obtain desire properties of nanoparticles you can follow some particular techniques only. Some techniques will give high yield but you can lose those requirements. Keep in this mind and select suitable method for your desired nanoparticles synthesis and you can get lot of information form literature.

Supercritical fluid technology.....media milling...spray drying

about 2 years ago I got interesting answers by the same question you can look at it:

https://www.researchgate.net/post/How_is_it_possible_make_mass_production_of_nanomaterials?_tpcectx=profile_questions

No general answer for your question.

From sol-gel process scaling up is difficult (for economic reasons) because you must work with highly dilute solutions.

It is much easier working with nano-emulsions or NLC´s. Just have just to reproduce working conditions of lab-scale tests in a different scale (Unit Operations scaling-up theory).